MEMS介绍

1 What’s happening in the world of MEMS?MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre (i.e. 0.02 to 1.0 mm). They usually consist of a central unit that processes data (the microprocessor) and several components that interact with the surroundings such as micro-sensors.[1]At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects suchas electrostatics and wetting dominate over volume effects such as inertia or thermal mass.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 tomake 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.Applications∙Inkjet printers, which use piezoelectrics or thermal bubble ejection to deposit ink on paper.∙Accelerometers in modern cars for a large number of purposesincluding airbag deployment in collisions.∙Accelerometers and MEMS gyroscopes in radio controlled, or autonomous, helicopters, planes and multirotors (also known as drones), used for automatically sensing and balancing flying characteristics of roll, pitch and yaw.∙Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone, various Nokia mobile phone models, various HTC PDA models)[16] 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 gyroscopes used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger dynamic stability control[17]∙MEMS microphones in portable devices, e.g., mobile phones, head sets and laptops. ∙Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors∙Displays e.g., the 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 micro-scanners∙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 Micro Total Analysis (biosensor, chemosensor), or embedded in medical devicese.g. stents.[18]∙Interferometric modulator display (IMOD) applications in consumer electronics (primarily di splays 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,[19] electrostatic and electromagnetic micro harvesters.∙Micromachined Ultrasound Transducer including Piezoelectric Micromachined Ultrasonic Transducers[20][21] and Capacitive Micromachined Ultrasonic Transducers.2.How did MEMS impact on this application in performance ,cost, or volume production?SizeSize reduction is achieved by significantly reducing the bond padsand their required overhead, (e.g. ESD protection) from the die realestate. This is accomplished with MEMS vias that ohmically connectthe MEMS to the underlying CMOS directly. The vias shown in Figure4 are only 3 µm in diameter. In a typical comparison such as thatshown in Table 2, the integrated approach can have four times fewerbond pads than a two-chip approach.PerformanceIn sensors that respond with a change in position (e.g. accelerometer, gyroscope, pressure), the preferred method of measuring that change in applications that are sensitive to powerconsumption is to measure a changein capacitance. Approaches that measure a change in resistance or frequency tend towards higher power consumption. A second consideration in the performance of the device is the parasitic coupling of interfering signals. Whether the objective is to reduce the EMI cross section or shield from coupling to undesired signals like clock orcommunication, the MEMS via approach has a significant advantage over running long traces to bond wires between two chips. The intimate coupling of the MEMS to CMOS is inherently much easier to safeguard against interference.ConclusionThe integrated monolithic, single-chip process and structural design enables m-Cube to ship the world’s smallest integrated accelerometer in volume. It can achieve this size without sacrificing performance or features. The savings from reduced size, lower testing costs, and lower assembly costs also enable this integrated approach to be very cost effective. While this approach has some advantages in the smartphone and gaming-market, it offers an attractive path of continued innovation especially for designers of wearable and smart clothing.。