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125-596: Integrals in the time domain implicitly demand a stable and accurate clock for the quantification of elapsed time. Inertial navigation is a self-contained navigation technique in which measurements provided by accelerometers and gyroscopes are used to track the position and orientation of an object relative to a known starting point, orientation and velocity. Inertial measurement units (IMUs) typically contain three orthogonal rate-gyroscopes and three orthogonal accelerometers, measuring angular velocity and linear acceleration respectively. By processing signals from these devices it

250-480: A magnetometer which is commonly used as a heading reference. Some IMUs, like Adafruit's 9-DOF IMU, include additional sensors like temperature. Typical configurations contain one accelerometer, gyro, and magnetometer per axis for each of the three principal axes: pitch, roll and yaw . IMUs are often incorporated into Inertial Navigation Systems , which utilize the raw IMU measurements to calculate attitude, angular rates, linear velocity, and position relative to

375-453: A vibrating structure gyroscope to detect changes in heading and the odometer pickup to measure distance covered along the vehicle's track. This type of system is much less accurate than a higher-end INS, but it is adequate for the typical automobile application where GPS is the primary navigation system and dead reckoning is only needed to fill gaps in GPS coverage when buildings or terrain block

500-540: A GPS receiver to work when GPS-signals are unavailable, such as in tunnels, inside buildings, or when electronic interference is present. IMUs are used in VR headsets and smartphones , and also in motion tracked game controllers like the Wii Remote . An inertial measurement unit works by detecting linear acceleration using one or more accelerometers and rotational rate using one or more gyroscopes . Some also include

625-444: A boron-doped glass wafer is bonded to a semiconductor wafer, usually silicon; thermocompression bonding, wherein an intermediary thin-film material layer is used to facilitate wafer bonding; and eutectic bonding, wherein a thin-film layer of gold is used to bond two silicon wafers. Each of these methods have specific uses depending on the circumstances. Most wafer bonding processes rely on three basic criteria for successfully bonding:

750-416: A certain direction vector were to measure a plane's acceleration as 5 m/s for 1 second, then after that 1 second the guidance computer would deduce that the plane must be traveling at 5 m/s and must be 2.5 m from its initial position (assuming v 0 =0 and known starting position coordinates x 0 , y 0 , z 0 ). If combined with a mechanical paper map or a digital map archive (systems whose output

875-565: A competing technology for use in motion capture technology. An IMU is at the heart of the balancing technology used in the Segway Personal Transporter . In a navigation system, the data reported by the IMU is fed into a processor which calculates altitude, velocity and position. A typical implementation referred to as a Strap Down Inertial System integrates angular rate from the gyroscope to calculate angular position. This

1000-405: A cooling liquid or a dry laser process called stealth dicing . Bulk micromachining is the oldest paradigm of silicon-based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures. Silicon is machined using various etching processes . Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that changed

1125-440: A flotation chamber to mount a gyrostabilized platform. These systems can have very high precisions (e.g., Advanced Inertial Reference Sphere ). Like all gyrostabilized platforms, this system runs well with relatively slow, low-power computers. The fluid bearings are pads with holes through which pressurized inert gas (such as helium) or oil presses against the spherical shell of the platform. The fluid bearings are very slippery and

1250-694: A gimballed system. That is, it must integrate the vehicle's attitude changes in pitch, roll and yaw, as well as gross movements. Gimballed systems could usually do well with update rates of 50–60 Hz. However, strapdown systems normally update about 2000 Hz. The higher rate is needed to let the navigation system integrate the angular rate into an attitude accurately. The data updating algorithms ( direction cosines or quaternions ) involved are too complex to be accurately performed except by digital electronics. However, digital computers are now so inexpensive and fast that rate gyro systems can now be practically used and mass-produced. The Apollo lunar module used

1375-508: A global reference frame. The IMU equipped INS forms the backbone for the navigation and control of many commercial and military vehicles, such as crewed aircraft, missiles, ships, submarines, and satellites. IMUs are also essential components in the guidance and control of uncrewed systems such as UAVs , UGVs , and UUVs . Simpler versions of INSs termed Attitude and Heading Reference Systems utilize IMUs to calculate vehicle attitude with heading relative to magnetic north. The data collected from

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1500-454: A gyroscope system can sometimes also be inferred simply from its position history (e.g., GPS). This is, in particular, the case with planes and cars, where the velocity vector usually implies the orientation of the vehicle body. For example, Honeywell 's Align in Motion is an initialization process where the initialization occurs while the aircraft is moving, in the air or on the ground. This

1625-487: A gyroscopic element (for maintaining an absolute angular reference). Angular accelerometers measure how the vehicle is rotating in space. Generally, there is at least one sensor for each of the three axes: pitch (nose up and down), yaw (nose left and right) and roll (clockwise or counter-clockwise from the cockpit). Linear accelerometers measure non-gravitational accelerations of the vehicle. Since it can move in three axes (up and down, left and right, forward and back), there

1750-458: A hole with curved sidewalls as with isotropic etching. Hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide ( SiO 2 , also known as BOX for SOI), usually in 49% concentrated form, 5:1, 10:1 or 20:1 BOE ( buffered oxide etchant ) or BHF (Buffered HF). They were first used in medieval times for glass etching. It was used in IC fabrication for patterning the gate oxide until

1875-448: A mask for the underlying substrate. Photolithography is typically used with metal or other thin film deposition, wet and dry etching. Sometimes, photolithography is used to create structure without any kind of post etching. One example is SU8 based lens where SU8 based square blocks are generated. Then the photoresist is melted to form a semi-sphere which acts as a lens. Electron beam lithography (often abbreviated as e-beam lithography)

2000-674: A millimetre (i.e., 0.02 to 1.0 mm), although components arranged in arrays (e.g., digital micromirror devices ) can be more than 1000 mm . They usually consist of a central unit that processes data (an integrated circuit chip such as microprocessor ) and several components that interact with the surroundings (such as microsensors ). Because of the large surface area to volume ratio of MEMS, forces produced by ambient electromagnetism (e.g., electrostatic charges and magnetic moments ), and fluid dynamics (e.g., surface tension and viscosity ) are more important design considerations than with larger scale mechanical devices. MEMS technology

2125-610: A mixture of the two remains. In the summer of 1952, Dr. Richard Battin and Dr. J. Halcombe "Hal" Laning, Jr. , researched computational based solutions to guidance and undertook the initial analytical work on the Atlas inertial guidance in 1954. Other key figures at Convair were Charlie Bossart, the Chief Engineer, and Walter Schweidetzky, head of the guidance group. Schweidetzky had worked with von Braun at Peenemünde during World War II. The initial Delta guidance system assessed

2250-553: A number of MOSFET microsensors were developed for measuring physical, chemical, biological and environmental parameters. The term "MEMS" was introduced in 1986. S.C. Jacobsen (PI) and J.E. Wood (Co-PI) introduced the term "MEMS" by way of a proposal to DARPA (15 July 1986), titled "Micro Electro-Mechanical Systems (MEMS)", granted to the University of Utah. The term "MEMS" was presented by way of an invited talk by S.C. Jacobsen, titled "Micro Electro-Mechanical Systems (MEMS)", at

2375-435: A process in which a material is removed from a target, and deposited on a surface. Techniques to do this include the process of sputtering , in which an ion beam liberates atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and evaporation , in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in

2500-448: A quadratic error growth in position. A constant error in attitude rate (gyro) results in a quadratic error growth in velocity and a cubic error growth in position. A very wide variety of IMUs exists, depending on application types, with performance ranging: To get a rough idea, this means that, for a single, uncorrected accelerometer, the cheapest (at 100 mg) loses its ability to give 50-meter accuracy after around 10 seconds, while

2625-715: A research report from SEMI and Yole Development and is forecasted to reach $ 72 billion by 2011. Companies with strong MEMS programs come in many sizes. Larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics. Smaller firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins. Both large and small companies typically invest in R&;D to explore new MEMS technology. The market for materials and equipment used to manufacture MEMS devices topped $ 1 billion worldwide in 2006. Materials demand

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2750-411: A side effect on size and mass. A wireless IMU is known as a WIMU. Microelectromechanical systems MEMS ( micro-electromechanical systems ) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres to

2875-422: A silicon substrate, and etch rates are 3–6 times higher than wet etching. After preparing a large number of MEMS devices on a silicon wafer , individual dies have to be separated, which is called die preparation in semiconductor technology. For some applications, the separation is preceded by wafer backgrinding in order to reduce the wafer thickness. Wafer dicing may then be performed either by sawing using

3000-408: A single transformer to power the platform. Some small missiles have powered the platform with light from a window or optic fibers to the motor. A research topic is to suspend the platform with pressure from exhaust gases. Data is returned to the outside world via the transformers, or sometimes LEDs communicating with external photodiodes . Lightweight digital computers permit the system to eliminate

3125-458: A strapdown system in its backup Abort Guidance System (AGS). Strapdown systems are nowadays commonly used in commercial and military applications (aircraft, ships, ROVs , missiles , etc.). State-of-the-art strapdown systems are based upon ring laser gyroscopes , fibre optic gyrocopes or hemispherical resonator gyroscopes . They are using digital electronics and advanced digital filtering techniques such as Kalman filter . The orientation of

3250-414: A vacuum system. Chemical deposition techniques include chemical vapor deposition (CVD), in which a stream of source gas reacts on the substrate to grow the material desired. This can be further divided into categories depending on the details of the technique, for example LPCVD (low-pressure chemical vapor deposition) and PECVD ( plasma-enhanced chemical vapor deposition ). Oxide films can also be grown by

3375-535: A wide range of applications. These products include "tuning fork gyros". Here, the gyro is designed as an electronically driven tuning fork, often fabricated out of a single piece of quartz or silicon. Such gyros operate in accordance with the dynamic theory that when an angle rate is applied to a translating body, a Coriolis force is generated. This system is usually integrated on a silicon chip. It has two mass-balanced quartz tuning forks, arranged "handle-to-handle" so forces cancel. Aluminum electrodes evaporated onto

3500-625: Is "plasmaless", is purely chemical and spontaneous and is often operated in pulsed mode. Models of the etching action are available, and university laboratories and various commercial tools offer solutions using this approach. Modern VLSI processes avoid wet etching, and use plasma etching instead. Plasma etchers can operate in several modes by adjusting the parameters of the plasma. Ordinary plasma etching operates between 0.1 and 5 Torr. (This unit of pressure, commonly used in vacuum engineering, equals approximately 133.3 pascals.) The plasma produces energetic free radicals, neutrally charged, that react at

3625-469: Is a dry vapor phase isotropic etch for silicon originally applied for MEMS in 1995 at University of California, Los Angeles. Primarily used for releasing metal and dielectric structures by undercutting silicon, XeF 2 has the advantage of a stiction -free release unlike wet etchants. Its etch selectivity to silicon is very high, allowing it to work with photoresist, SiO 2 , silicon nitride, and various metals for masking. Its reaction to silicon

3750-405: Is a linear accelerometer for each axis. A computer continually calculates the vehicle's current position. First, for each of the six degrees of freedom (x,y,z and θ x , θ y and θ z ), it integrates over time the sensed acceleration, together with an estimate of gravity, to calculate the current velocity. Then it integrates the velocity to calculate the current position. Inertial guidance

3875-419: Is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs. This exposed region can then be removed or treated providing

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4000-402: Is a process used in the electronic industry to selectively remove parts of a thin film. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist", on the substrate. A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist. Diamond patterning is a method of forming diamond MEMS. It

4125-460: Is a special subclass of RIE that is growing in popularity. In this process, etch depths of hundreds of micrometers are achieved with almost vertical sidewalls. The primary technology is based on the so-called "Bosch process", named after the German company Robert Bosch, which filed the original patent, where two different gas compositions alternate in the reactor. Currently, there are two variations of

4250-421: Is accomplished using GPS and an inertial reasonableness test, thereby allowing commercial data integrity requirements to be met. This process has been FAA certified to recover pure INS performance equivalent to stationary alignment procedures for civilian flight times up to 18 hours. It avoids the need for gyroscope batteries on aircraft. Less-expensive navigation systems, intended for use in automobiles, may use

4375-421: Is achieved by the lithographic application of diamond films to a substrate such as silicon. The patterns can be formed by selective deposition through a silicon dioxide mask, or by deposition followed by micromachining or focused ion beam milling . There are two basic categories of etching processes: wet etching and dry etching . In the former, the material is dissolved when immersed in a chemical solution. In

4500-456: Is based on both sensors and IMU models. Complexity for these models will then be chosen according to the needed performance and the type of application considered. Ability to define this model is part of sensors and IMU manufacturers know-how. Sensors and IMU models are computed in factories through a dedicated calibration sequence using multi-axis turntables and climatic chambers. They can either be computed for each individual product or generic for

4625-471: Is calculated from the previous calculated position and the measured acceleration and angular velocity, these errors accumulate roughly proportionally to the time since the initial position was input. Even the best accelerometers, with a standard error of 10 micro-g, would accumulate a 50-meter (164-ft) error within 17 minutes. Therefore, the position must be periodically corrected by input from some other type of navigation system. Accordingly, inertial navigation

4750-424: Is capable of generating holes in thin films without any development process. Structural depth can be defined either by ion range or by material thickness. Aspect ratios up to several 10 can be reached. The technique can shape and texture materials at a defined inclination angle. Random pattern, single-ion track structures and an aimed pattern consisting of individual single tracks can be generated. X-ray lithography

4875-461: Is developed using a moving plate or sensing element, which changes the capacitance. Ohmic switches are controlled by electrostatically controlled cantilevers. Ohmic MEMS switches can fail from metal fatigue of the MEMS actuator (cantilever) and contact wear, since cantilevers can deform over time. The fabrication of MEMS evolved from the process technology in semiconductor device fabrication , i.e.

5000-521: Is difficult without computers. The desire to use inertial guidance in the Minuteman missile and Project Apollo drove early attempts to miniaturize computers. Inertial guidance systems are now usually combined with satellite navigation systems through a digital filtering system. The inertial system provides short term data, while the satellite system corrects accumulated errors of the inertial system. An inertial guidance system that will operate near

5125-771: Is distinguished from molecular nanotechnology or molecular electronics in that the latter two must also consider surface chemistry . The potential of very small machines was appreciated before the technology existed that could make them (see, for example, Richard Feynman 's famous 1959 lecture There's Plenty of Room at the Bottom ). MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics . These include molding and plating, wet etching ( KOH , TMAH ) and dry etching ( RIE and DRIE), electrical discharge machining (EDM), and other technologies capable of manufacturing small devices. They merge at

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5250-403: Is fused with the gravity vector measured by the accelerometers in a Kalman filter to estimate attitude. The attitude estimate is used to transform acceleration measurements into an inertial reference frame (hence the term inertial navigation) where they are integrated once to get linear velocity, and twice to get linear position. For example, if an IMU installed in an aeroplane moving along

5375-534: Is generally known as a moving map display since the guidance system position output is often taken as the reference point, resulting in a moving map), the guidance system could use this method to show a pilot where the plane is located geographically in a certain moment, as with a GPS navigation system, but without the need to communicate with or receive communication from any outside components, such as satellites or land radio transponders, though external sources are still used in order to correct drift errors, and since

5500-525: Is held annually in October in Germany. The publications of all DGON ISA conferences over the last more than 60 years are accessible. All inertial navigation systems suffer from integration drift: small errors in the measurement of acceleration and angular velocity are integrated into progressively larger errors in velocity, which are compounded into still greater errors in position. Since the new position

5625-476: Is highly anisotropic. On the other hand, it tends to display poor selectivity. Reactive-ion etching (RIE) operates under conditions intermediate between sputter and plasma etching (between 10 and 10  Torr). Deep reactive-ion etching (DRIE) modifies the RIE technique to produce deep, narrow features. In reactive-ion etching (RIE), the substrate is placed inside a reactor, and several gases are introduced. A plasma

5750-433: Is necessary to compensate for three main resulting behaviors: Decreasing these errors tends to push IMU designers to increase processing frequencies, which becomes easier using recent digital technologies. However, developing algorithms able to cancel these errors requires deep inertial knowledge and strong intimacy with sensors/IMU design. On the other hand, if suspension is likely to enable IMU performance increase, it has

5875-500: Is possible to track the position and orientation of a device. An inertial navigation system includes at least a computer and a platform or module containing accelerometers , gyroscopes , or other motion-sensing devices. The INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.) accompanied with the initial orientation and thereafter computes its own updated position and velocity by integrating information received from

6000-533: Is resistant to the wet etchants. This has been used in MEWS pressure sensor manufacturing for example. Etching progresses at the same speed in all directions. Long and narrow holes in a mask will produce v-shaped grooves in the silicon. The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate. Some single crystal materials, such as silicon, will have different etching rates depending on

6125-428: Is struck in the gas mixture using an RF power source, which breaks the gas molecules into ions. The ions accelerate towards, and react with, the surface of the material being etched, forming another gaseous material. This is known as the chemical part of reactive ion etching. There is also a physical part, which is similar to the sputtering deposition process. If the ions have high enough energy, they can knock atoms out of

6250-428: Is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film (called the resist ), ("exposing" the resist) and of selectively removing either exposed or non-exposed regions of the resist ("developing"). The purpose, as with photolithography , is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. It

6375-405: Is throughput, i.e., the very long time it takes to expose an entire silicon wafer or glass substrate. A long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. Also, the turn-around time for reworking or re-design is lengthened unnecessarily if the pattern is not being changed the second time. It is known that focused- ion beam lithography has

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6500-416: Is used to oxidize ("ash") photoresist and facilitate its removal. Ion milling, or sputter etching , uses lower pressures, often as low as 10  Torr (10 mPa). It bombards the wafer with energetic ions of noble gases, often Ar+, which knock atoms from the substrate by transferring momentum. Because the etching is performed by ions, which approach the wafer approximately from one direction, this process

6625-421: Is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining. Some common commercial applications of MEMS include: The global market for micro-electromechanical systems, which includes products such as automobile airbag systems, display systems and inkjet cartridges totaled $ 40 billion in 2006 according to Global MEMS/Microsystems Markets and Opportunities,

6750-452: Is usually used to supplement other navigation systems, providing a higher degree of accuracy than is possible with the use of any single system. For example, if, in terrestrial use, the inertially tracked velocity is intermittently updated to zero by stopping, the position will remain precise for a much longer time, a so-called zero velocity update . In aerospace particularly, other measurement systems are used to determine INS inaccuracies, e.g.

6875-427: Is very accurate. However it is still relatively expensive due to the cost of the precision ground and polished hollow quartz hemispheres. Northrop Grumman currently manufactures IMUs ( inertial measurement units ) for spacecraft that use HRGs. These IMUs have demonstrated extremely high reliability since their initial use in 1996. Safran manufactures large numbers of HRG based inertial navigation systems dedicated to

7000-534: Is vulnerable to gimbal lock . The primary guidance system of the Apollo spacecraft used a three-axis gyrostabilized platform, feeding data to the Apollo Guidance Computer . Maneuvers had to be carefully planned to avoid gimbal lock. Gimbal lock constrains maneuvering and it would be beneficial to eliminate the slip rings and bearings of the gimbals. Therefore, some systems use fluid bearings or

7125-550: The Space Shuttle , open loop guidance was used to guide the Shuttle from lift-off until Solid Rocket Booster (SRB) separation. After SRB separation the primary Space Shuttle guidance is named PEG (Powered Explicit Guidance). PEG takes into account both the Q system and the predictor-corrector attributes of the original "Delta" System (PEG Guidance). Although many updates to the Shuttle's navigation system had taken place over

7250-417: The U.S. Army Research Laboratory reported a method to merge measurements from 10 pairs of MEMS gyroscope and accelerometers (plus occasional GPS), reducing the positional error by two thirds for a projectile. The algorithm can correct for systemic biases in individual sensors, using both GPS and a heuristic based on the gun-firing acceleration force. If one sensor consistently over or underestimates distance,

7375-561: The pressure reference system was developed to use one numerical integration of the angular rate measurements. Estimation theory in general and Kalman filtering in particular, provide a theoretical framework for combining information from various sensors. One of the most common alternative sensors is a satellite navigation radio such as GPS , which can be used for all kinds of vehicles with direct sky visibility. Indoor applications can use pedometers , distance measurement equipment, or other kinds of position sensors . By properly combining

7500-832: The C-5A which utilized the triple INS configuration, similar to the 747. The KC-135A fleet was fitted with a single Carousel IV-E system that could operate as a stand-alone INS or can be aided by the AN/APN-81 or AN/APN-218 Doppler radar . Some special-mission variants of the C-135 were fitted with dual Carousel IV-E INSs. ARINC Characteristic 704 defines the INS used in commercial air transport. INSs contain Inertial Measurement Units (IMUs) which have angular and linear accelerometers (for changes in position); some IMUs include

7625-497: The DRIE. The first variation consists of three distinct steps (the original Bosch process) while the second variation only consists of two steps. In the first variation, the etch cycle is as follows: In the 2nd variation, steps (i) and (iii) are combined. Both variations operate similarly. The C 4 F 8 creates a polymer on the surface of the substrate, and the second gas composition ( SF 6 and O 2 ) etches

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7750-868: The Delco Electronics Div. of General Motors Corp. were awarded the joint contract for design and production of the Apollo Guidance and Navigation systems for the Command Module and the Lunar Module. Delco produced the IMUs ( Inertial Measurement Units ) for these systems, Kollsman Instrument Corp. produced the Optical Systems, and the Apollo Guidance Computer was built by Raytheon under subcontract. For

7875-464: The Earth, since they did not know what direction the car was facing relative to the Earth when they felt the accelerations. However, by tracking both the current angular velocity of the system and the current linear acceleration of the system measured relative to the moving system, it is possible to determine the linear acceleration of the system in the inertial reference frame. Performing integration on

8000-515: The Honeywell LaseRefV inertial navigation systems uses GPS and air data computer outputs to maintain required navigation performance . The navigation error rises with the lower sensitivity of the sensors used. Currently, devices combining different sensors are being developed, e.g. attitude and heading reference system . Because the navigation error is mainly influenced by the numerical integration of angular rates and accelerations,

8125-673: The IEEE Micro Robots and Teleoperators Workshop, Hyannis, MA Nov. 9–11, 1987. The term "MEMS" was published by way of a submitted paper by J.E. Wood, S.C. Jacobsen, and K.W. Grace, titled "SCOFSS: A Small Cantilevered Optical Fiber Servo System", in the IEEE Proceedings Micro Robots and Teleoperators Workshop, Hyannis, MA Nov. 9–11, 1987. CMOS transistors have been manufactured on top of MEMS structures. There are two basic types of MEMS switch technology: capacitive and ohmic . A capacitive MEMS switch

8250-459: The IMU's sensors allows a computer to track craft's position, using a method known as dead reckoning . This data is usually presented in Euler vectors representing the angles of rotation in the three primary axis or a quaternion . In land vehicles, an IMU can be integrated into GPS based automotive navigation systems or vehicle tracking systems , giving the system a dead reckoning capability and

8375-553: The V2 provided many innovations as an integrated platform with closed loop guidance. At the end of the war von Braun engineered the surrender of 500 of his top rocket scientists, along with plans and test vehicles, to the Americans. They arrived at Fort Bliss, Texas in 1945 under the provisions of Operation Paperclip and were subsequently moved to Huntsville, Alabama , in 1950 where they worked for U.S. Army rocket research programs. In

8500-514: The ability to determine developmental levels of individuals when in motion by identifying specificity and sensitivity of specific parameters associated with running. Some gaming systems such as the remote controls for the Nintendo Wii use IMUs to measure motion. Low-cost IMUs have enabled the proliferation of the consumer drone industry. They are also frequently used for sports technology (technique training), and animation applications. They are

8625-576: The ability to gather as much accurate data as possible about the vehicle's current speed, turn rate, heading, inclination and acceleration, in combination with the vehicle's wheel speed sensor output and, if available, reverse gear signal, for purposes such as better traffic collision analysis. Besides navigational purposes, IMUs serve as orientation sensors in many consumer products. Almost all smartphones and tablets contain IMUs as orientation sensors. Fitness trackers and other wearables may also include IMUs to measure motion, such as running. IMUs also have

8750-429: The advent of spacecraft , guided missiles , and commercial airliners . Early German World War II V2 guidance systems combined two gyroscopes and a lateral accelerometer with a simple analog computer to adjust the azimuth for the rocket in flight. Analog computer signals were used to drive four graphite rudders in the rocket exhaust for flight control. The GN&C (Guidance, Navigation, and Control) system for

8875-435: The angular displacement, the system's current orientation is known at all times. This can be thought of as the ability of a blindfolded passenger in a car to feel the car turn left and right or tilt up and down as the car ascends or descends hills. Based on this information alone, the passenger knows what direction the car is facing, but not how fast or slow it is moving, or whether it is sliding sideways. Accelerometers measure

9000-537: The basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes. One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere from one micrometre to about 100 micrometres. The NEMS process is the same, although the measurement of film deposition ranges from a few nanometres to one micrometre. There are two types of deposition processes, as follows. Physical vapor deposition ("PVD") consists of

9125-546: The best accelerometer (at 10 μg) loses its 50-meter accuracy after around 17 minutes. The accuracy of the inertial sensors inside a modern inertial measurement unit (IMU) has a more complex impact on the performance of an inertial navigation system (INS). Gyroscope and accelerometer sensor behavior is often represented by a model based on the following errors, assuming they have the proper measurement range and bandwidth: All these errors depend on various physical phenomena specific to each sensor technology. Depending on

9250-438: The capability of writing extremely fine lines (less than 50 nm line and space has been achieved) without proximity effect. However, because the writing field in ion-beam lithography is quite small, large area patterns must be created by stitching together the small fields. Ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. It

9375-450: The car has turned and how it has accelerated and decelerated since, then they can accurately know the current orientation, position, and velocity of the car at any time. Inertial navigation is used in a wide range of applications including the navigation of aircraft, tactical and strategic missiles, spacecraft, submarines and ships. It is also embedded in some mobile phones for purposes of mobile phone location and tracking. Recent advances in

9500-460: The construction of microelectromechanical systems (MEMS) have made it possible to manufacture small and light inertial navigation systems. These advances have widened the range of possible applications to include areas such as human and animal motion capture . Inertial navigation systems are used in many different moving objects. However, their cost and complexity place constraints on the environments in which they are practical for use. To support

9625-416: The crystalline silicon at approximately equal rates. Anisotropic wet etchants preferably etch along certain crystal planes at faster rates than other planes, thereby allowing more complicated 3-D microstructures to be implemented. Wet anisotropic etchants are often used in conjunction with boron etch stops wherein the surface of the silicon is heavily doped with boron resulting in a silicon material layer that

9750-469: The crystallographic orientation of the substrate. This is known as anisotropic etching and one of the most common examples is the etching of silicon in KOH (potassium hydroxide), where Si <111> planes etch approximately 100 times slower than other planes ( crystallographic orientations ). Therefore, etching a rectangular hole in a (100)-Si wafer results in a pyramid shaped etch pit with 54.7° walls, instead of

9875-419: The difference in capacitance between the two tines of a fork, the system can determine the rate of angular motion. Inertial measurement unit An inertial measurement unit ( IMU ) is an electronic device that measures and reports a body's specific force , angular rate, and sometimes the orientation of the body, using a combination of accelerometers , gyroscopes , and sometimes magnetometers . When

10000-519: The difference in position from a reference trajectory. A velocity to be gained (VGO) calculation is made to correct the current trajectory with the objective of driving VGO to zero. The mathematics of this approach were fundamentally valid, but dropped because of the challenges in accurate inertial guidance and analog computing power. The challenges faced by the Delta efforts were overcome by the Q system (see Q-guidance ) of guidance. The Q system's revolution

10125-723: The early 1950s, the US government wanted to insulate itself against over-dependency on the German team for military applications, including the development of a fully domestic missile guidance program. The MIT Instrumentation Laboratory (later to become the Charles Stark Draper Laboratory , Inc.) was chosen by the Air Force Western Development Division to provide a self-contained guidance system backup to Convair in San Diego for

10250-488: The first production Carousel systems for the early models (-100, -200 and -300) of the 747 aircraft. The 747 utilized three Carousel systems operating in concert for reliability purposes. The Carousel system and derivatives thereof were subsequently adopted for use in many other commercial and military aircraft. The USAF C-141 was the first military aircraft to utilize the Carousel in a dual system configuration, followed by

10375-419: The forks and the underlying chip both drive and sense the motion. The system is both manufacturable and inexpensive. Since quartz is dimensionally stable, the system can be accurate. As the forks are twisted about the axis of the handle, the vibration of the tines tends to continue in the same plane of motion. This motion has to be resisted by electrostatic forces from the electrodes under the tines. By measuring

10500-449: The gimbals, creating strapdown systems, so called because their sensors are simply strapped to the vehicle. This reduces the cost, eliminates gimbal lock , removes the need for some calibrations and increases the reliability by eliminating some of the moving parts. Angular rate sensors called rate gyros measure the angular velocity of the vehicle. A strapdown system needs a dynamic measurement range several hundred times that required by

10625-432: The guidance system is continually integrating acceleration with respect to time to calculate velocity and position (see dead reckoning ) , any measurement errors, however small, are accumulated over time. This leads to 'drift': an ever-increasing difference between where the system thinks it is located and the actual location. Due to integration a constant error in acceleration results in a linear error growth in velocity and

10750-442: The industrial production of sensors, ink-jet nozzles, and other devices. But in many cases the distinction between these two has diminished. A new etching technology, deep reactive-ion etching , has made it possible to combine good performance typical of bulk micromachining with comb structures and in-plane operation typical of surface micromachining . While it is common in surface micromachining to have structural layer thickness in

10875-531: The industrialization of surface micromachining and has realized the co-integration of MEMS and integrated circuits. Wafer bonding involves joining two or more substrates (usually having the same diameter) to one another to form a composite structure. There are several types of wafer bonding processes that are used in microsystems fabrication including: direct or fusion wafer bonding, wherein two or more wafers are bonded together that are usually made of silicon or some other semiconductor material; anodic bonding wherein

11000-451: The inertial accelerations (using the original velocity as the initial conditions) using the correct kinematic equations yields the inertial velocities of the system and integration again (using the original position as the initial condition) yields the inertial position. In our example, if the blindfolded passenger knew how the car was pointed and what its velocity was before they were blindfolded, and if they are able to keep track of both how

11125-560: The information from an INS and other systems ( GPS ), the errors in position and velocity are stable . Furthermore, INS can be used as a short-term fallback while GPS signals are unavailable, for example when a vehicle passes through a tunnel. In 2011, GPS jamming at the civilian level became a governmental concern. The relative ease in ability to jam these systems has motivated the military to reduce navigation dependence on GPS technology. Because inertial navigation sensors do not depend on radio signals unlike GPS, they cannot be jammed. In 2012,

11250-515: The last 30 years (ex. GPS in the OI-22 build), the guidance core of the Shuttle GN&;C system had evolved little. Within a crewed system, there is a human interface needed for the guidance system. As astronauts are the customer for the system, many new teams were formed that touch GN&C as it is a primary interface to "fly" the vehicle. One example of a popular INS for commercial aircraft

11375-562: The latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant. Wet chemical etching consists of the selective removal of material by dipping a substrate into a solution that dissolves it. The chemical nature of this etching process provides good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully. Wet etching can be performed using either isotropic wet etchants or anisotropic wet etchants. Isotropic wet etchant etch in all directions of

11500-410: The linear acceleration and angular velocity applied to the system. Since it requires no external reference (after initialization), it is immune to jamming and deception. Gyroscopes measure the angular displacement of the sensor frame with respect to the inertial reference frame . By using the original orientation of the system in the inertial reference frame as the initial condition and integrating

11625-512: The linear acceleration of the moving vehicle in the sensor or body frame, but in directions that can only be measured relative to the moving system (since the accelerometers are fixed to the system and rotate with the system, but are not aware of their own orientation). This can be thought of as the ability of a blindfolded passenger in a car to feel themself pressed back into their seat as the vehicle accelerates forward or pulled forward as it slows down; and feel themself pressed down into their seat as

11750-414: The magnetometer is included, IMUs are referred to as IMMUs. IMUs are typically used to maneuver modern vehicles including motorcycles, missiles, aircraft (an attitude and heading reference system ), including uncrewed aerial vehicles (UAVs), among many others, and spacecraft , including satellites and landers . Recent developments allow for the production of IMU-enabled GPS devices. An IMU allows

11875-473: The material to be etched without a chemical reaction. It is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. By changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical. Deep reactive ion etching (DRIE)

12000-413: The motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized. An INS can detect a change in its geographic position (a move east or north, for example), a change in its velocity (speed and direction of movement) and a change in its orientation (rotation about an axis). It does this by measuring

12125-476: The nanoscale into nanoelectromechanical systems (NEMS) and nanotechnology . An early example of a MEMS device is the resonant-gate transistor, an adaptation of the MOSFET , developed by Robert A. Wickstrom for Harvey C. Nathanson in 1965. Another early example is the resonistor, an electromechanical monolithic resonator patented by Raymond J. Wilfinger between 1966 and 1971. During the 1970s to early 1980s,

12250-533: The new Atlas intercontinental ballistic missile (Construction and testing were completed by Arma Division of AmBosch Arma). The technical monitor for the MIT task was engineer Jim Fletcher, who later served as NASA Administrator. The Atlas guidance system was to be a combination of an on-board autonomous system and a ground-based tracking and command system. The self-contained system finally prevailed in ballistic missile applications for obvious reasons. In space exploration,

12375-466: The pilot entered in the aircraft longitude and latitude at takeoff, the unit would show the pilot the longitude and latitude of the aircraft in relation to the ground. Positional tracking systems like GPS can be used to continually correct drift errors (an application of the Kalman filter ). A major disadvantage of using IMUs for navigation is that they typically suffer from accumulated error. Because

12500-401: The platform keep the same orientation while the vehicle rotates around it). There are two gyroscopes (usually) on the platform. Two gyroscopes are used to cancel gyroscopic precession , the tendency of a gyroscope to twist at right angles to an input torque. By mounting a pair of gyroscopes (of the same rotational inertia and spinning at the same speed in opposite directions) at right angles

12625-502: The platform uses similar strip-shaped transformers to read the varying magnetic fields produced by the transformers wrapped around the spherical platform. Whenever a magnetic field changes shape, or moves, it will cut the wires of the coils on the external transformer strips. The cutting generates an electric current in the external strip-shaped coils and electronics can measure that current to derive angles. Cheap systems sometimes use bar codes to sense orientations and use solar cells or

12750-555: The position update frequency allowed by inertial navigation systems can be higher than the vehicle motion on the map display can be perceived as smooth. This method of navigation is called dead reckoning . One of the earliest units was designed and built by Ford Instrument Company for the USAF to help aircraft navigate in flight without any input from outside the aircraft. Called the Ground-Position Indicator , once

12875-491: The precessions are cancelled and the platform will resist twisting. This system allows a vehicle's roll, pitch and yaw angles to be measured directly at the bearings of the gimbals. Relatively simple electronic circuits can be used to add up the linear accelerations, because the directions of the linear accelerometers do not change. The big disadvantage of this scheme is that it uses many expensive precision mechanical parts. It also has moving parts that can wear out or jam and

13000-767: The process step was replaced by RIE. Hydrofluoric acid is considered one of the more dangerous acids in the cleanroom . Electrochemical etching (ECE) for dopant-selective removal of silicon is a common method to automate and to selectively control etching. An active p–n diode junction is required, and either type of dopant can be the etch-resistant ("etch-stop") material. Boron is the most common etch-stop dopant. In combination with wet anisotropic etching as described above, ECE has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. Selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon. Xenon difluoride ( XeF 2 )

13125-457: The range of 2 μm, in HAR silicon micromachining the thickness can be from 10 to 100 μm. The materials commonly used in HAR silicon micromachining are thick polycrystalline silicon, known as epi-poly, and bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also have been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding

13250-565: The same silicon wafer. The original surface micromachining concept was based on thin polycrystalline silicon layers patterned as movable mechanical structures and released by sacrificial etching of the underlying oxide layer. Interdigital comb electrodes were used to produce in-plane forces and to detect in-plane movement capacitively. This MEMS paradigm has enabled the manufacturing of low cost accelerometers for e.g. automotive air-bag systems and other applications where low performance and/or high g-ranges are sufficient. Analog Devices has pioneered

13375-623: The satellite signals. If a standing wave is induced in a hemispheric resonant structure and then the resonant structure is rotated, the spherical harmonic standing wave rotates through an angle different from the quartz resonator structure due to the Coriolis force. The movement of the outer case with respect to the standing wave pattern is proportional to the total rotation angle and can be sensed by appropriate electronics. The system resonators are machined from fused quartz due to its excellent mechanical properties. The electrodes that drive and sense

13500-401: The sensor industry in the 1980s and 1990s. Surface micromachining uses layers deposited on the surface of a substrate as the structural materials, rather than using the substrate itself. Surface micromachining was created in the late 1980s to render micromachining of silicon more compatible with planar integrated circuit technology, with the goal of combining MEMS and integrated circuits on

13625-409: The spherical platform can turn freely. There are usually four bearing pads, mounted in a tetrahedral arrangement to support the platform. In premium systems, the angular sensors are usually specialized transformer coils made in a strip on a flexible printed circuit board . Several coil strips are mounted on great circles around the spherical shell of the gyrostabilized platform. Electronics outside

13750-404: The standing waves are deposited directly onto separate quartz structures that surround the resonator. These gyros can operate in either a whole angle mode (which gives them nearly unlimited rate capability) or a force rebalance mode that holds the standing wave in a fixed orientation with respect to the gyro housing (which gives them much better accuracy). This system has almost no moving parts and

13875-417: The substrate. The polymer is immediately sputtered away by the physical part of the etching, but only on the horizontal surfaces and not the sidewalls. Since the polymer only dissolves very slowly in the chemical part of the etching, it builds up on the sidewalls and protects them from etching. As a result, etching aspect ratios of 50 to 1 can be achieved. The process can easily be used to etch completely through

14000-433: The surface of the earth must incorporate Schuler tuning so that its platform will continue pointing towards the center of the Earth as a vehicle moves from place to place. Some systems place the linear accelerometers on a gimballed gyrostabilized platform. The gimbals are a set of three rings, each with a pair of bearings initially at right angles. They let the platform twist about any rotational axis (or, rather, they let

14125-428: The surface of the wafer. Since neutral particles attack the wafer from all angles, this process is isotropic. Plasma etching can be isotropic, i.e., exhibiting a lateral undercut rate on a patterned surface approximately the same as its downward etch rate, or can be anisotropic, i.e., exhibiting a smaller lateral undercut rate than its downward etch rate. Such anisotropy is maximized in deep reactive ion etching. The use of

14250-399: The system can adjust the corrupted sensor's contributions to the final calculation. Inertial navigation systems were originally developed for rockets . American rocketry pioneer Robert Goddard experimented with rudimentary gyroscopic systems. Goddard's systems were of great interest to contemporary German pioneers including Wernher von Braun . The systems entered more widespread use with

14375-556: The targeted applications and to be able to make the proper sensor choice, it is very important to consider the needs regarding stability, repeatability, and environment sensitivity (mainly thermal and mechanical environments), on both short and long terms. Targeted performance for applications is, most of the time, better than a sensor's absolute performance. However, sensor performance is repeatable over time, with more or less accuracy, and therefore can be assessed and compensated to enhance its performance. This real-time performance enhancement

14500-408: The technique of thermal oxidation , in which the (typically silicon) wafer is exposed to oxygen and/or steam, to grow a thin surface layer of silicon dioxide . Patterning is the transfer of a pattern into a material. Lithography in a MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material

14625-405: The term anisotropy for plasma etching should not be conflated with the use of the same term when referring to orientation-dependent etching. The source gas for the plasma usually contains small molecules rich in chlorine or fluorine. For instance, carbon tetrachloride ( CCl 4 ) etches silicon and aluminium, and trifluoromethane etches silicon dioxide and silicon nitride. A plasma containing oxygen

14750-504: The use of inertial technology in the best way, already in 1965 a technical working group for Inertial Sensors had been established in Germany to bring together the users, the manufacturers and the researchers of inertial sensors. This working group has been continuously developed and today it is known as DGON ISA Inertial Sensors and Application Symposium, the leading conference for inertial technologies for more than 60 years. This Symposium DGON / IEEE ISA with about 200 international attendees

14875-420: The vehicle accelerates up a hill or rise up out of their seat as the car passes over the crest of a hill and begins to descend. Based on this information alone, they know how the vehicle is accelerating relative to itself; that is, whether it is accelerating forward, backward, left, right, up (toward the car's ceiling), or down (toward the car's floor), measured relative to the car, but not the direction relative to

15000-464: The wafers to be bonded are sufficiently flat; the wafer surfaces are sufficiently smooth; and the wafer surfaces are sufficiently clean. The most stringent criteria for wafer bonding is usually the direct fusion wafer bonding since even one or more small particulates can render the bonding unsuccessful. In comparison, wafer bonding methods that use intermediary layers are often far more forgiving. Both bulk and surface silicon micromachining are used in

15125-422: The whole production. Calibration will typically improve a sensor's raw performance by at least two decades. High performance IMUs, or IMUs designed to operate under harsh conditions, are very often suspended by shock absorbers. These shock absorbers are required to master three effects: Suspended IMUs can offer very high performance, even when submitted to harsh environments. However, to reach such performance, it

15250-520: Was developed for manufacturing integrated circuits , and is also used for creating nanotechnology architectures. The primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer range. This form of maskless lithography has found wide usage in photomask -making used in photolithography , low-volume production of semiconductor components, and research & development. The key limitation of electron beam lithography

15375-553: Was presented at the first Technical Symposium on Ballistic Missiles held at the Ramo-Wooldridge Corporation in Los Angeles on 21 and 22 June 1956. The Q system was classified information through the 1960s. Derivations of this guidance are used for today's missiles. In February 1961 NASA awarded MIT a contract for preliminary design study of a guidance and navigation system for the Apollo program . MIT and

15500-486: Was the Delco Carousel , which provided partial automation of navigation in the days before complete flight management systems became commonplace. The Carousel allowed pilots to enter 9 waypoints at a time and then guided the aircraft from one waypoint to the next using an INS to determine aircraft position and velocity. Boeing Corporation subcontracted the Delco Electronics Div. of General Motors to design and build

15625-420: Was to bind the challenges of missile guidance (and associated equations of motion) in the matrix Q. The Q matrix represents the partial derivatives of the velocity with respect to the position vector. A key feature of this approach allowed for the components of the vector cross product (v, xdv, /dt) to be used as the basic autopilot rate signals—a technique that became known as cross-product steering . The Q-system

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