On -chip high voltage generation using mechanical oscillators.

Abstract

The building blocks of microsystems, like discharge based chemical sensors, electrostatic actuators, electrokinetic pumps and Geiger counters, need high voltages for their operation. In order to meet this need for high voltages, the most convenient method is to step up voltage from a DC power source (battery) using an inductor and a switch. The approach taken is to use a microfabricated mechanical relay using a high aspect ratio process that allows the fabrication of the high voltage generator and other micro-devices on the same dice. In order to use a micro-relay without electronics, a fully mechanical oscillator has been developed using electrothermal actuators. This actuator operates from a low voltage (less than 5 V) DC supply and is used to generate high voltages using an inductive element. Two generations of the oscillator were developed. The first generation, made from electroplated copper using a UV-LIGA process uses both thermal and mechanical hysteresis to effect a time delay. Its design conforms to constraints imposed by high aspect ratio lithography. The second generation, besides incorporating design modifications, is made from a noble metal switch alloy (platinum-rhodium) and, therefore, conforms to substantially different design rules. The ability to make released in-plane microstructures from any conductive material is realized through the development of the Reverse Damascene process that uses mico-electro-discharge machining. The process allows the fabrication of bio-compatible stainless steel devices. In addition a model for the mechanical oscillator has been developed that uses the finite difference method to model the dynamics of the electrothermal actuator. The measured frequency of the oscillator is in the range of 100 Hz, while the duty cycle varies between about 0.2 to 0.3. The power consumption is about 100 mW. Modeling results predict the maximum frequency to be about 1000 Hz. The oscillator when connected to an inductor generates high voltage spikes measured up to 1200 V. A capacitor connected across output, along with a diode in the circuit path leads to the generation of high voltage DC. A peak DC voltage of 276.5 V at 76 mW of power has been measured.