MEMS

MEMS
Name	Microelectromechanical systems
Caption	A die containing a Bosch accelerometer.
Acronym	MEMS
Classification	Microtechnology, Nanotechnology
Related fields	Electrical engineering, Mechanical engineering, Materials science
Notable developers	NovaSensor, Analog Devices, Texas Instruments
Key applications	Automotive airbags, smartphones, inkjet printers, projection displays

MEMS. Microelectromechanical systems are miniaturized devices that integrate mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication techniques. These systems, typically ranging in size from a micrometer to a millimeter, merge the computational power of microelectronics with the perception and control capabilities of microsensors and microactuators. This convergence enables the creation of sophisticated systems-on-a-chip for a vast array of applications, from consumer electronics to biomedical devices.

Overview

The core principle involves creating miniature mechanical structures using processes derived from the semiconductor industry, particularly those used to fabricate integrated circuits. These structures can interact with their environment by sensing physical phenomena like acceleration, pressure, or chemical species, or by performing actions such as moving micromirrors or dispensing microfluidic droplets. Key enabling technologies include surface micromachining, bulk micromachining, and the development of specialized thin films. The field is closely related to microsystems technology in Europe and is considered a precursor to more advanced nanotechnology and NEMS.

Fabrication

Fabrication primarily utilizes modified semiconductor device fabrication methods, with photolithography being a fundamental step to pattern layers. Surface micromachining builds structures by depositing and etching successive layers of structural material and sacrificial material on a substrate, a technique advanced by researchers like Roger T. Howe at the University of California, Berkeley. Bulk micromachining selectively removes material from the silicon wafer itself to create membranes, beams, and other features. More specialized techniques include LIGA, which uses X-ray lithography and electroplating to create high-aspect-ratio structures, and wafer bonding for creating complex three-dimensional devices and sealed cavities.

Materials

While single-crystal silicon is the dominant material due to its excellent mechanical properties and compatibility with CMOS processes, many other materials are integral. Polysilicon is widely used as a structural layer in surface micromachining. Silicon dioxide and silicon nitride serve as insulating layers and sacrificial materials. For specific applications, materials like piezoelectric lead zirconate titanate, shape-memory alloys such as Nitinol, and polymers like SU-8 photoresist are employed. Advanced research explores the use of carbon nanotubes and graphene for next-generation devices.

Applications

Applications are pervasive across numerous industries. In consumer electronics, accelerometers and gyroscopes enable screen rotation and image stabilization in products from Apple and Samsung. The automotive industry uses pressure sensors for manifold monitoring and accelerometers for airbag deployment. Texas Instruments employs a digital micromirror device for digital light processing in projectors. In healthcare, MEMS are found in lab-on-a-chip devices for blood analysis and miniature pressure sensors for intracranial monitoring. Other uses include RF MEMS switches for telecommunications and microbolometers for infrared imaging in systems from FLIR Systems.

Design and modeling

Design requires specialized computer-aided design tools that account for multi-domain physics, including electrostatics, fluid dynamics, and structural mechanics. Software suites from companies like COMSOL and Ansys are commonly used for finite element analysis and system-level simulation. Modeling must consider unique micro-scale effects such as stiction, residual stress in thin films, and squeeze-film damping. The design process often involves close collaboration between teams specializing in IC layout, mechanical design, and process integration to ensure manufacturability and performance.

History

The conceptual foundations were laid in the 1950s and 1960s with the invention of the integrated circuit by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor. The first recognizable devices emerged in the 1970s, such as the micromachined silicon pressure sensor developed at IBM. A significant milestone was the demonstration of the resonant-gate transistor, a precursor to many sensor designs. The 1980s saw the development of surface micromachining at the University of California, Berkeley, leading to the first integrated MEMS. The field expanded rapidly in the 1990s with commercialization efforts by companies like Analog Devices, which successfully integrated a MEMS accelerometer with control electronics for automotive airbags, paving the way for widespread adoption.

Category:Microtechnology Category:Electrical engineering Category:Mechanical engineering