Field-Assisted MEMS Pull-In Voltage Compensation Using ALD Electrets

F.K. Chowdhury, M. Tabib-Azar
University of Utah, US

Keywords: MEMS switch, electrets, attractive and repulsive electrostatics

Summary:

This article discusses scaled MEMS switches that rely on ALD SiO2-Al2O3 electrets that enable both attractive and repulsive field effects. As a result, these devices present field-assisted pull-in/pull-out voltage modulation which renders our switches highly desirable in harsh environment such as high temperature and high ionizing radiations – where pull-in voltage variation is seen – for in-situ voltage compensation/correction. Some applications include troubled reactors (where CMOS cannot operate due to high temperature or I-R) like Chernobyl and Fukushima or at high temperatures encountered inside combustion engines. When charged electrets are incorporated into the MEMS switches via an ALD SiO2-Al2O3 stack we observe field-assisted pull-in voltage modulation. From our experiments we concluded that the electrets were negatively charged owing to the trend in decreasing pull-in voltage seen when progressively decreasing negative gate voltages were applied and confirmed this by measurement of surface charge densities which was measured at ~12pC/cm2. Prolonged switching of these devices with 500nm gaps resulted in >1270 cycles of successful operation. The full article will discuss design and characterization of the above MEMS logic devices and other related circuits for construction of “mechanical” processors. Reproducibility data as well as yield and lifetime to failure will be reported.