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 adjacent the base element and a free
end adjacent the free end tip. 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, .DELTA.T.sub.1b, that is greater than a first
deflector layer free end temperature increase, .DELTA.T.sub.1f. 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, .DELTA.T.sub.2b
that is greater than a second deflector layer free end temperature
increase, .DELTA.T.sub.2f. 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
.tau..sub.B. The thermal actuator is activated by a heat pulses of
duration .tau..sub.p wherein .tau..sub.p <1/2 .tau..sub.B.
