Microelectromechanical systems (MEMS) is one of the fastest growing technologies in microelectronics, and is of great interest for military and aerospace applications. Accelerometers are the earliest and most developed representatives of MEMS. First demonstrated in 1979, micromachined accelerometers were used in automobile industry for air bag crash-sensing applications since 1990. In 1999, MEMS accelerometers were used in NASA-JPL Mars Microprobe [1].

The most developed accelerometers for airbag crash-sensing are rated for a full range of ± 50 G. The range of sensitivity for accelerometers required for military or aerospace applications is much larger, varying from 20,000 G (to measure acceleration during gun and ballistic munition launches), and to 10^-6 G, when used as guidance sensors (to measure attitude and position of a spacecraft). The presence of moving parts on the surface of chip is specific to MEMS, and particularly, to accelerometers. This characteristic brings new reliability issues to micromachined accelerometers, including cyclic fatigue cracking of polysilicon cantilevers and springs, mechanical stresses that are caused by packaging and contamination in the internal cavity of the package. Studies of fatigue cracks initiation and growth in polysilicon [2, 3] showed that the fatigue damage may influence MEMS device performance, and the presence of water vapor significantly enhances crack initiation and growth.

Environmentally induced failures, particularly, failures due to thermal cycling and mechanical shock are considered as one of major reliability concerns in MEMS [1]. These environmental conditions are also critical for space applications of the parts. For example, the Mars pathfinder mission had experienced 80 mechanical shock events during pyrotechnic separation processes [4].

In general, most of the analyses of the failure mechanisms in MEMS have been performed using test structures. However, a comprehensive qualification of MEMS, requires experimental data obtained using real parts. In this respect, endurance characteristics of the accelerometers with respect to temperature cycling and mechanical shock is of great interest in their evaluation for space applications.

In the present study, thermo-mechanical stability of commercially available, mass production accelerometers (ADXL250) available from Analog Devices was evaluated, by subjecting them to multiple temperature cycles in the range from –65 ° C to +150 ° C and mechanical shocks of 2000 G in X and Z directions.