MEMS

• 微小電気機械システム

関

micro electric mechanical system

PrepTutorEJDIC

1. Maine / Middle English / Middle East

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/10/06 11:54:10」(JST)

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[Wiki ja表示]

半導体プロセスを用いて作成されたギア（左下）とダニ（右上）の電子顕微鏡写真。（サンディア国立研究所 SUMMiTTM Technologies の好意による www.mems.sandia.gov）

蟻と歯車

LIGAプロセスで製造された光スイッチ

MEMS（メムス、Micro Electro Mechanical Systems）は、機械要素部品、センサ、アクチュエータ、電子回路を一つのシリコン基板、ガラス基板、有機材料などの上に微細加工技術によって集積化したデバイスを指す。プロセス上の制約や材料の違いなどにより、機械構造と電子回路が別なチップになる場合があるが、このようなハイブリッドの場合もMEMSという。

主要部分はLIGAプロセスや半導体集積回路作製技術にて作るが、立体形状や可動構造を形成するための犠牲層エッチングプロセスをも含む。

本来、MEMSはセンサなどの既存のデバイスの代替を主な目的として研究開発が進められていたが、近年はMEMSにしか許されない環境下での実験手段として注目されている。例えば、電子顕微鏡の中は高真空で微小な空間だが、MEMSならばその小ささと機械的性質を利用して電子顕微鏡下での実験を行うことができる。また、DNAや生体試料などのナノ・マイクロメートルの物質を操作・捕獲・分析するツールとしても活躍している。

現在、製品として市販されている物としては、インクジェットプリンタのヘッド、圧力センサ、加速度センサ、ジャイロスコープ、プロジェクタ・写真焼付機等に利用されるDMD、光造形式3Dプリンターやレーザープロジェクタ等に使用されるガルバノメータなどがあり、徐々に応用範囲は拡大しつつある。

市場規模が拡大して応用分野も多岐にわたるため、期待は大きく、第二のDRAMと言われたこともある。

歴史

歴史的には古くから機械構造を半導体製作技術で作製する方法が行われてきた。1951年にはRCA社によりシャドーマスクが製作され、1963年には既に豊田中央研究所により半導体圧力センサが発表されている。1970年頃にはスタンフォード大学でNASAの委託研究でガスクロマトグラフがシリコンウエハ上に作成された。MEMSの定義にもよるが、いくつかの文献では世界で最初のMEMSは1967年に発表されたH. C. Nathansonによる「The Resonant Gate Transistor」となっている。ただし、圧力センサもMEMSに分類されるので豊田中研の半導体圧力センサもMEMSと考えられ、どれが世界初であるかについては議論が分かれる。

このような微細な機械構造が注目を集めるきっかけとなったのは1987年のTransducers'87で発表されたマイクロギアやタービンである。その後、マイクロモータ、櫛歯型アクチュエータなどの発明により脚光を浴びる。初期の段階では動くだけで良かったが最近では応用を見据えたデバイスが主流である。

現在では後述のように多様な応用先があるため、MEMS応用の市場規模は日本国内だけでも数千億円にものぼり、将来的には数兆円規模になると言われている。

プロセスの見地では、最近まで半導体集積回路技術と近いサーフェイスマイクロマシニングが主流であったが、ICP-RIEによる深掘りエッチングやウエハ接合、LIGAプロセス技術などMEMS特有のプロセス技術の発展によりバルクマイクロマシニングが主流となってきている。
CMOS回路と組み合わせたデバイスはCMOS回路とのプロセス技術の整合性からサーフェイスマイクロマシニングを用いる場合が多いが、SOIウエハを用いてバルクマイクロマシニングとCMOS回路を組み合わせたデバイスも多くなってきている。

代表的なMEMSデバイス

市販されている代表的なデバイス

• プリンタヘッド: 特にインクジェットプリンタ用
• 圧力センサ
• 加速度センサ
• ジャイロスコープ
• 光スキャナ (ガルバノメータ)
• AFM用カンチレバー
• 流路モジュール
• デジタルミラーデバイス(DMD)
• HDDのヘッド
• DNAチップ
• 光スイッチ
• ボロメータ型赤外線撮像素子
• 波長可変レーザー (共振器を可変長化する)
• 光変調器

主な応用先

研究段階の物や期待される応用分野

高周波応用

主に微小な高周波スイッチや共振器を実現する。

機械的な高周波スイッチの場合、半導体の高周波スイッチより動作速度は遅いものの、低損失のスイッチが実現できる。

共振器は小型で高いQ値を持つものが作製可能である。水晶を用いても高いQ値を実現できるが、シリコンで作製できるため集積回路との集積化が容易である。

• 高周波スイッチ
• フィルタ
• 発振器用振動子：水晶振動子と置き換えて使う

光応用

• 光通信用光スイッチ
• 光スキャナ
• 投射型ディスプレイ
• 電子ペーパ
• ヘッドマウントディスプレイ

流体応用

• マイクロバルブ
• マイクロ流路

生化学応用

• DNA分析チップ
• 蛋白質分析チップ

医療応用

• 血液検査チップ
• 能動カテーテル
• ドラッグデリバリシステム

センサ

• 圧力センサ
• 触覚センサ
• 慣性センサ
  • 加速度センサ
  • ジャイロセンサ
• 化学センサ
• マイクロフォン：ECMの代わりに使う

宇宙応用

• マイクロスラスタ
• マイクロカロリーメータ

MEMSにおける特徴的なプロセス技術

集積回路作製技術以外にMEMSで用いられる技術

大きな分類

• バルクマイクロマシニング(Bulk Micromachining)
• サーフェイスマイクロマシニング(Surface Micromachining)

エッチング技術

• 犠牲層エッチング
• 深掘りエッチング:ICP-RIE
• 異方性エッチング
• 多段エッチング

リソグラフィ技術

• フォトリソグラフィ
• LIGA
• 3次元リソグラフィ
• 電子線直描
• 厚膜レジスト

接合技術

• 直接接合
• 陽極接合

MEMSに用いられるアクチュエータ

静電力を用いたもの

構造が簡単で小型化に向いている。発生力は他の方法に比べて小さい。MEMSでは最も使われる駆動原理

• 平行平板型静電アクチュエータ
• 櫛歯型静電アクチュエータ
• スクラッチドライブアクチュエータ (Scratch Drive Actuator:SDA)
• 静電マイクロモータ

電磁力を用いたもの

コイルや磁石が必要になるため、静電型に比べ構造が複雑で大きいが、大きな力を発生することができる。ヒステリシスやドリフトを伴うこともある。

• 電磁力アクチュエータ
• 磁歪アクチュエータ

圧電効果を用いたもの

大きな力を発生できるが、変位が小さい。

• 圧電型アクチュエータ
• 圧電バイモルフ

熱歪みを用いたもの

構造が簡単で、大きな力を発生できるが、ドリフトなどの不安定要素がある

• 熱バイモルフアクチュエータ
• 熱膨張型

その他

• 圧縮気体を用いたもの
• 電気分解を用いたもの

ソフトウェア

MEMSは微小構造物なので、解析を行う際には汎用的なシミュレーションソフトウェアでは、微小構造による特有の現象を考慮していないため正確な解析を行うことができない。近年ではPCのスペックも向上しているため汎用シミュレーションでも解析が可能であると紹介されているが、静電デバイスやシステム解析といった総合的なMEMS設計を考えると汎用ソフトウェアより専門ソフトウェアに優位性がある。

専門ソフトウェア

・IntelliSuite　(IntelliSense社)[1]

・CoventorWare

文献

• James B. Angell; Stephen C. Terry; Phillip W. Barth (April 1983). “Silicon Micromechanical Devices”. サイエンティフィック・アメリカン 248 (4): 44 - 55. 
• J.B.エンジェル、S.C.テリー、P.W.バース「シリコン基板に組み込んだマイクロセンサー」、『サイエンス』、日経サイエンス社、1983年6月号、 18頁。

関連項目

• 江刺正喜
• 藤田博之
• マイクロマシン、マイクロボット
• マイクロファブリケーション
• Transducers
• NEMS
• micro-TAS
• センサネットワーク
• スマートダスト(Smart dust)
• MEMS-IGZOディスプレイ
• ナノトライボロジー

外部リンク

• 動画のMEMSとそのアプリケーションに.
• アナログデバイセズ MEMSセンサー

wiki en

[Wiki en表示]

"MEMS" redirects here. For other uses, see MEMS (disambiguation).

Proposal submitted to DARPA in 1986 first introducing the term "microelectromechanical systems"

MEMS microcantilever resonating inside a scanning electron microscope

Ultrasonic Transducers from IPMS Dresden vibrating at 8Mhz measured by Digital Holographic Microscopy

Microelectromechanical systems (MEMS, also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems and the related micromechatronics) is the technology of microscopic devices, particularly those with moving parts. It merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines in Japan, or micro systems technology (MST) in Europe.

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 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 mm². They usually consist of a central unit that processes data (the 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 is distinguished from molecular nanotechnology or molecular electronics in that the latter 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), electro discharge machining (EDM), and other technologies capable of manufacturing small devices. An early example of a MEMS device is the resonistor, an electromechanical monolithic resonator patented by Raymond J. Wilfinger, and the resonant gate transistor developed by Harvey C. Nathanson.

Materials for MEMS manufacturing

The fabrication of MEMS evolved from the process technology in semiconductor device fabrication, i.e. the basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes.

Silicon

Silicon is the material used to create most integrated circuits used in consumer electronics in the modern industry. The economies of scale, ready availability of inexpensive high-quality materials, and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking.

Polymers

Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to produce. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding, embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.

Metals

Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability. Metals can be deposited by electroplating, evaporation, and sputtering processes. Commonly used metals include gold, nickel, aluminium, copper, chromium, titanium, tungsten, platinum, and silver.

Ceramics

The nitrides of silicon, aluminium and titanium as well as silicon carbide and other ceramics are increasingly applied in MEMS fabrication due to advantageous combinations of material properties. AlN crystallizes in the wurtzite structure and thus shows pyroelectric and piezoelectric properties enabling sensors, for instance, with sensitivity to normal and shear forces. TiN, on the other hand, exhibits a high electrical conductivity and large elastic modulus, making it possible to implement electrostatic MEMS actuation schemes with ultrathin membranes. Moreover, the high resistance of TiN against biocorrosion qualifies the material for applications in biogenic environments and in biosensors.

MEMS basic processes

Deposition processes

One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometres to about 100 micrometres. There are two types of deposition processes, as follows.

Physical deposition

Physical vapor deposition ("PVD") consists of 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 a vacuum system.

Chemical deposition

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 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

Patterning in MEMS is the transfer of a pattern into a material.

Lithography

Lithography in 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 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 a mask for the underlying substrate. Photolithography is typically used with metal or other thin film deposition, wet and dry etching.

Electron beam lithography

Main article: Electron beam lithography

Electron beam lithography (often abbreviated as e-beam lithography) 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 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 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.

Ion beam lithography

It is known that focused-ion beam lithography has 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

Ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. It is capable to generate 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 10⁴ can be reached. The technique can shape and texture materials at a defined inclination angle. Random pattern, single-ion track structures and aimed pattern consisting of individual single tracks can be generated.

X-ray lithography

X-ray lithography is a process used in 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

A simple way to carve or create patterns on the surface of nanodiamonds without damaging them could lead to a new photonic devices.

Diamond patterning is a method of forming diamond MEMS. It 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.

Etching processes

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 the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant.

Wet etching

Main article: Etching (microfabrication)

Wet chemical etching consists in selective removal of material by dipping a substrate into a solution that dissolves it. The chemical nature of this etching process provides a good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully.

Isotropic etching

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.

Anisotropic etching

Some single crystal materials, such as silicon, will have different etching rates depending on 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 a hole with curved sidewalls as with isotropic etching.

HF 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 the process step was replaced by RIE.

Hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. It penetrates the skin upon contact and it diffuses straight to the bone. Therefore, the damage is not felt until it is too late.

Electrochemical etching

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.

Dry etching

Xenon difluoride

Xenon difluoride (XeF
2) 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 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.

Plasma etching

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 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 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 (CCl4) etches silicon and aluminium, and trifluoromethane etches silicon dioxide and silicon nitride. A plasma containing oxygen is used to oxidize ("ash") photoresist and facilitate its removal.

Ion milling, or sputter etching, uses lower pressures, often as low as 10−4 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 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 10–3 and 10−1 Torr). Deep reactive-ion etching (DRIE) modifies the RIE technique to produce deep, narrow features.

Reactive ion etching (RIE)

Main article: Reactive-ion etching

In reactive-ion etching (RIE), the substrate is placed inside a reactor, and several gases are introduced. A plasma 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 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.

Main article: Deep reactive ion etching

Deep RIE (DRIE) is a special subclass of RIE that is growing in popularity. In this process, etch depths of hundreds of micrometres 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 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:

(i) SF
6 isotropic etch;
(ii) C
4F
8 passivation;
(iii) SF
6 anisoptropic etch for floor cleaning.

In the 2nd variation, steps (i) and (iii) are combined.

Both variations operate similarly. The C
4F
8 creates a polymer on the surface of the substrate, and the second gas composition (SF
6 and O
2) etches 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 a silicon substrate, and etch rates are 3–6 times higher than wet etching.

Die preparation

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 a cooling liquid or a dry laser process called stealth dicing.

MEMS manufacturing technologies

Bulk micromachining

Main article: Bulk micromachining

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. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that changed the sensor industry in the 1980s and 90's.

Surface micromachining

Main article: Surface micromachining

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 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 the industrialization of surface micromachining and has realized the co-integration of MEMS and integrated circuits.

High aspect ratio (HAR) silicon micromachining

Both bulk and surface silicon micromachining are used in 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 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 is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining.

Microelectromechanical systems chip, sometimes called "lab on a chip"

Applications

A Texas Instruments DMD chip for cinema projection

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Measuring mechanical properties of a gold stripe (width ~1 µm) using MEMS inside a transmission electron microscope.

Some common commercial applications of MEMS include:

• Inkjet printers, which use piezoelectrics or thermal bubble ejection to deposit ink on paper.
• Accelerometers in modern cars for a large number of purposes including airbag deployment and electronic stability control.
• Accelerometers and MEMS gyroscopes in remote controlled, or autonomous, helicopters, planes and multirotors (also known as drones), used for automatically sensing and balancing flying characteristics of roll, pitch and yaw. MEMS magnetic field sensor (magnetometer) may also be incorporated in such devices to provide directional heading. MEMS gyroscopes are also used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger electronic stability control
• Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (virtually all smartphones, various HTC PDA models) and a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs to park the hard disk head when free-fall is detected, to prevent damage and data loss.
• MEMS microphones in portable devices, e.g., mobile phones, head sets and laptops. The market for smart microphones includes smartphones, wearable devices, smart home and automotive applications.
• Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors
• Displays e.g., the digital micromirror device (DMD) chip in a projector based on DLP technology, which has a surface with several hundred thousand micromirrors or single micro-scanning-mirrors also called microscanners
• Optical switching technology, which is used for switching technology and alignment for data communications
• Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemosensor), or embedded in medical devices e.g. stents.
• Interferometric modulator display (IMOD) applications in consumer electronics (primarily displays for mobile devices), used to create interferometric modulation − reflective display technology as found in mirasol displays
• Fluid acceleration such as for micro-cooling
• Micro-scale energy harvesting including piezoelectric, electrostatic and electromagnetic micro harvesters.
• Micromachined ultrasound transducers.

Industry structure

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, a research report from SEMI and Yole Developpement 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 is driven by substrates, making up over 70 percent of the market, packaging coatings and increasing use of chemical mechanical planarization (CMP). While MEMS manufacturing continues to be dominated by used semiconductor equipment, there is a migration to 200 mm lines and select new tools, including etch and bonding for certain MEMS applications.

See also

• Brain–computer interface
• Cantilever - one of the most common forms of MEMS.
• Electrostatic motors used where coils are difficult to fabricate
• Kelvin probe force microscope
• MEMS sensor generations
• MEMS thermal actuator, MEMS actuation created by thermal expansion
• Micro-opto-electromechanical systems (MOEMS), MEMS including optical elements
• Photoelectrowetting, MEMS optical actuation using photo-sensitive wetting
• Micropower, Hydrogen generators, gas turbines, and electrical generators made of etched silicon
• Millipede memory, a MEMS technology for non-volatile data storage of more than a terabit per square inch
• Nanoelectromechanical systems are similar to MEMS but smaller
• Scratch Drive Actuator, MEMS actuation using repeatedly applied voltage differences

UpToDate Contents

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★リンクテーブル★

リンク元	「微小電気機械システム」「micro electric mechanical system」
関連記事	「ME」「MEM」

「微小電気機械システム」

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英

micro electric mechanical system、MEMS

「micro electric mechanical system」

　　[★]

微小電気機械システム

関

MEMS

「ME」

　　[★]

• 医用電子工学、医用工学

関

medical electronics、medical engineering

　

「MEM」

　　[★]

• 基礎・地

関

minimal essential medium