Generation of electrically induced stimuli for MEMS self-test

A major task for the implementation of Built-In-Self-Test (BIST) strategies for MEMS is the generation of the test stimuli. These devices can work in different energy domains and are thus designed to sense signals which are g enerally not electrical. In this work, we describe, for different types of MEMS, how the required non-electrical test stimuli can be induced on-chip b y means of electrical signals. This provides the basis for adding BIST stra tegies for MEMS parts embedded in the coming generation of integrated syste ms. The on-chip test signal generation is illustrated for the case of MEMS transducers which exploit such physical principles as time-varying electros tatic capacitance, piezo-resistivity effect and Seebeck effect. These princ iples are used in devices such as accelerometers, infrared imagers, pressur e sensors or tactile sensors. For implementation, we have used two major ME MS technologies including CMOS-compatible bulk micromachining and surface m icromachining. We illustrate the ability to generate on-chip test stimuli a nd to implement a self-test strategy for the case of a complete application . This corresponds to an infrared imager that can be used in multiple appli cations such as overheating detection, night vision, and earth tracking for satellite positioning. The imager consists of an array of thermal pixels t hat sense an infrared radiation. Each pixel is implemented as a suspended m embrane that contains several thermopiles along the different support arms. The on-chip test signal generation proposed requires only slight modificat ions and allows a production test of the imager with a standard test equipm ent, without the need of special infrared sources and the associated optica l equipment. The test function can also be activated off-line in the field for validation and maintenance purposes.