Tapered multi-layer thermal actuator and method of operating same

Abstract

An apparatus for and method of operating a thermal actuator for a micromechanical device, especially a liquid drop emitter such as an ink jet printhead, is disclosed. The disclosed thermal actuator comprises a base element and a cantilevered element including a thermo-mechanical bender portion extending from the base element to a free end tip. The thermo-mechanical bender portion includes a barrier layer constructed of a dielectric material having low thermal conductivity, a first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion, and a second deflector layer constructed of a second electrically resistive material having a large coefficient of thermal expansion wherein the barrier layer is bonded between the first and second deflector layers. The thermo-mechanical bender portion further has a base end and base end width, w , adjacent the base element, and a free end and free end width, w , adjacent the free end tip, wherein the base end width is substantially greater than the free end width. A first heater resistor is formed in the first deflector layer and adapted to apply heat energy having a first spatial thermal pattern which results in a first deflector layer base end temperature increase, &Dgr;T , that is greater than a first deflector layer free end temperature increase, &Dgr;T . A second heater resistor is formed in the second deflector layer and adapted to apply heat energy having a second spatial thermal pattern which results in a second deflector layer base end temperature increase, &Dgr;T that is greater than a second deflector layer free end temperature increase, &Dgr;T . Application of an electrical pulse to either the first or second heater resistors causes deflection of the cantilevered element, followed by restoration of the cantilevered element to an initial position as heat diffuses through the barrier layer and the cantilevered element reaches a uniform temperature. For liquid drop emitter embodiments, the thermal actuator resides in a liquid-filled chamber that includes a nozzle for ejecting liquid. Application of electrical pulses to the heater resistors is used to adjust the characteristics of liquid drop emission. The barrier layer exhibits a heat transfer time constant &tgr; . The thermal actuator is activated by a heat pulses of duration &tgr; wherein &tgr; <&frac12;&tgr; .