CMOS Current Driver for Electrothermal MEMS Switches With Actuation and Diagnostic Circuitry

This paper presents an integrated CMOS current driver designed for electrothermal micro-electromechanical-systems (MEMS) switches, fabricated using a 0.18  \mu m Bipolar-CMOS-DMOS (BCD) process. Unlike conventional constant-voltage drivers typically employed for MEMS actuators with positive temperature coefficient of resistance (TCR), this driver adopts a constant-current actuation. This approach benefits series-connected array components, applications seeking enhanced electromigration control, as well as actuators exhibiting a negative TCR. The system includes a 6-bit programmable digital-to-analog converter, current multiplication circuits, and feedback diagnostic capabilities, enabling precise control and monitoring of actuator performance within a core area of 1.5 mm². The driver supports pulse-width modulation (PWM) to significantly reduce power consumption compared to DC actuation and implements a double-pulse strategy for accelerating switch activation times. Diagnostic circuits measure actuator resistance within ± 0.5  Ω and switching states to enhance reliability in safety-critical applications. Experimental validation confirmed that the driver successfully provides currents up to 110 mA with a resolution of 1.65 mA. At a minimum output voltage of 1.7 V, it can power electrothermal actuators with up to 775 mW under an 8 V supply voltage, corresponding to a power density of 517 mW/mm². The driver was demonstrated to successfully actuate a chevron-style MEMS switch in 3.5 ms and maintain contact with a 76.7 mA, 50 % PWM waveform at 1 kHz, reducing power consumption by 30.72 %.