Fully Integrated High Voltage MEMS Drivers in CMOS

Abstract

We present the design of a fully-integrated high-voltage MEMS driver with an on-chip charge pump in 65nm CMOS technology. Bulk CMOS is mainly limited by the breakdown voltage transistors as well as that of the well/substrate diode. To operate in a high voltage environment (in the order of 10V), we applied the NWell/Psub and DNWell/Psub diodes which satisfy the described conditions. The proposed charge pump is composed of a 4-stage charge pump, which demonstrates a four-fold voltage increment at the output. Also, the charge pump design features MOSFET to replace the diode to eliminate the efficiency loss due to the diode voltage drop. The high-voltage driver is designed to reduce the energy loss and handle the 10V charge pump output while preventing the CMOS transistor breakdown, capable of producing a 250-kHz square wave at 10 V. A chip prototype is fabricated in standard 65nm CMOS technology, with the 4-stage charge pump and high-voltage driver occupying 0.1 and 0.12 mm2, respectively. This work achieves a peak charge pumps efficiency of 68.6%, with an input parasitic sensor capacitance and the charge pump loading capacitance of 5pF and 67pF, respectively. By eliminating the discharging of the charge pump during the driver output transitions, the proposed driver achieves a driving efficiency of 40.86%, which is almost 9X improvement when compared with the state of the art. Keywords - Charge Pump; high voltage driver; high efficiency.