Micromachining and operation of a bistable electrothermal actuator

This paper presents the micromachining and operation of a new electrothermal micro-actuator, which possesses the advantage of being bistable without continually consuming power to maintain its state. This micro-actuator was fabricated in the Mitel 1.5 mu m CMOS technology, enabling integration with a microelectronics addressing circuit on the same chip. The post-processing employs a combination of anisotropic and isotropic etching using a liquid etchant (tetramethyl ammonium hydroxide (TMAH)), a gaseous etchant (xenon difluoride (XeF sub(2))), and a plasma etch step (carbon tetrafluoride (CF sub(4 ))) to release the actuator from the silicon substrate. The actuator consists of a cantilever beam structure composed of two bilayers, a short-circuit pad and an abutment. It uses the bimorph effect of these bilayers to actuate between ON and OFF states.