Micromachines: An Enabling Technology for the FutureDr. Alton Romig Jr.
President ASM International
Director, Microsystems Science, Technology and Components, Sandia National Laboratories
When one defines a "microsystem" one can consider a small living creature, such as a dust mite. Six characteristics that are present in the "system" are: Sensors, Intelligence (processing capability), Actuators, Power, Communication, and Self-Assembly. It is now possible to incorporate all of these characteristics into a single piece of Silicon; a multifunctional "system-on-a-chip" which can Sense (smart sensors), Think (process info - custom microprocessors), Communicate (laser optical), and Act (MEMS and IMEMS [Intelligent] Miniature Electro-Mechanical Systems).
Virtually, all components of such systems are batch fabricated onto a single silicon wafer, and require no assembly, making mass production very inexpensive. Monolithic parts are also extremely reliable. Process development (on the other hand) is very expensive. The fabrication process for the MEMS involves the following seven steps (repeated many times depending on complexity of the chip design). It is performed seperately from traditional CMOS processing on the same silicon wafer, by processing the wafer in a modular fashion.
1) Deposit layer of sacrificial oxide on single-crystal Si wafer.
2) Apply light sensitive photoresist, and expose using oxide mask of detail.
3) Develop the photoresist and etch away oxide not protected by the photoresist.
4) Strip off photoresist and deposit conformal layer of polysilicon.
5) Apply photoresist, and expose using polysilicon mask.
6) Develop the photoresist and etch away polysilicon not protected by photoresist.
7) Strip off photoresist and etch away sacrificial oxide to complete the feature.
An example of this technology being developed is "smart airbag sensors" which incorporate multi-axis accelerometers, a processor, and mechanical-photo latching to execute a "controlled" deployment of an airbag, in response to the nature of the impact, weight and trajectory of the passenger, etc. Other likely uses include Medical Pressure Sensors, Automotive Pressure Sensors, Smart Tires, ABS Sensors, Auto Navigation Gyros, Smart Munitions, Pacemakers, Machine Monitoring, Machine Control, Infusion Pumps, Industrial Valves, Fluid Meters, Ink-Jet Printers, and Optical Switches.
Details of Radiation Hard Sensor and MEMS working as an on-board weapons lock were presented. The device, which requires a 24-bit key code, is only 4 mm x 4 mm and is uneffected by radiation or EMF.