Microbeams with Electronically Controlled High Thermal Impedance

Abstract

In some MEMS (Micro-Electro-Mechanical Systems) applications, a tradeoff much be reached between the mechanical strength of a suspended microstructure and the thermal losses through the support beams. This is typically the case of suspended thermal MEMS, a major domain of application of CMOS-compatible bulk-micromachining technologies. This paper illustrates how suspended MEMS can be strengthened by means of additional support beams which can have a very high thermal impedance, thus having a very small impact in the thermal behavior of the microstructure. The high thermal impedance of a support beam is achieved through self-heating: an electronic control monitors the temperature drop and heats up the beam to reduce the heat flow. The control electronics of a beam is implemented using a single high-gain stage with auto-zeroing. A High Thermal Impedance Beam (HTIB) can be considered as a new MEMS design cell. We illustrate the use of this cell in the design of an Electro-Thermal Converter with long time constant, requiring several HTIB cells which can share the same control electronics. A single low-frequency high-gain stage is used, achieving 60 dB DC gain and DC offset and broadband noise below 100 μV, which is suitable for the ETC application.