Micromechanical and tribological characterization of doped single-crystal silicon and polysilicon films for microelectro
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Micromechanical and tribological characterization of doped single-crystal silicon and polysilicon films for microelectromechanical systems devices Bharat Bhushan and Xiaodong Li Computer Microtribology and Contamination Laboratory, Department of Mechanical Engineering, The Ohio State University, Columbus, Ohio 43210 (Received January 29, 1996; accepted September 18, 1996)
Microelectromechanical systems (MEMS) devices are made of doped single-crystal silicon, LPCVD polysilicon films, and other ceramic films. Very little is understood about tribology and mechanical characterization of these materials on micro- to nanoscales. Micromechanical and tribological characterization of p-type (lightly boron-doped) single-crystal silicon (referred to as “undoped”), p 1 -type ( boron doped) single-crystal silicon, polysilicon bulk, and n1 -type (phosphorous doped) LPCVD polysilicon films have been carried out. Hardness, elastic modulus, and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the undoped silicon and polysilicon bulk as well as n1 -type polysilicon film exhibit higher hardness and elastic modulus than the p 1 -type silicon. The polysilicon bulk and n1 -type polysilicon film exhibit the lowest friction and highest resistance to scratch and wear followed by the undoped silicon and with the poorest behavior of the p 1 -type silicon. During scratching, the p 1 -type silicon deforms like a ductile metal.
I. INTRODUCTION
Using established semiconductor (integrated circuit or IC) processing techniques, researchers have fabricated a wide range of miniature components (referred to as microelectromechanical systems or MEMS) such as pressure and acceleration sensors, linear actuators, valves, grippers, tweezers, motors, gear trains, turbines, nozzles, and pumps1–13 with dimensions of a couple to a couple-of-hundred microns. The emphasis to date has been the laboratory demonstration of individual components. Systems are being developed incorporating MEMS devices. Pressure and acceleration sensors are commercially used mainly in medical instrumentation and automobiles. For example, since 1993, acceleration sensors on a chip are used to sense automobile collisions and signal the need to deploy an airbag.12 MEMS sensors are used for the airbag not because of their miniature size but because semiconductor processing techniques can allow manufacturing at low cost with high reliability. Acceleration sensors for the air bag are a several billion dollarsyyear industry dominated by Lucas NovaSensor and Analog Devices. Texas Instruments uses deformable mirror arrays on microflextures as part of airline ticket laser printers and high-resolution projection displays. MEMS devices are being developed at an accelerated pace for super-compact and ultrahigh recording density magnetic disk drives. Horizontal thin-film heads with a
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