High-voltage devices and circuits fabricated using foundry CMOS for use with electrostatic MEM actuators

Abstract

Devices and circuits capable of high-voltage operation are necessary for the actuation of micromachined electrostatic structures that require high voltages (20–100 V). These high-voltage devices have traditionally been fabricated using specialized processes. Monolithic integration of the actuators with circuits, including the high-voltage drive, makes it important to provide high-voltage circuit elements in CMOS, which is often the process of choice for signal-processing circuits. Fabrication processes available through foundry services using standard CMOS are attractive to users with no or limited access to clean-room facilities. High-voltage n- and p-type MOS transistors have been fabricated using the 2.0 μm analog CMOS process available through the MOSIS foundry service. By using the n-well and the p-base layers as lightly doped drains, breakdown voltages are 120 V and −27 V for the NMOS and PMOS structures, respectively. The corresponding Early voltages are − 1000 V for the NMOS and 240 V for the PMOS devices. A simple differential amplifier using the high-voltage devices has been fabricated and used to drive all-aluminum electrostatic actuator structures. A first-level SPICE model has also been derived for the high-voltage transistors.