Multi-layer thermal actuator with optimized heater length and method of operating same

A method for operating a thermal actuator, said thermal actuator comprising a base element, a cantilevered element extending a length L from the base element and residing in a first position, the cantilevered element including first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion and patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L;

• a second deflector layer;
• a barrier layer, having a heat transfer time constant of τB, bonded between the first deflector layer and the second deflector layer;
• and a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to heat the first deflector layer, the method for operating comprising:
• (a) applying to the first pair of electrodes an electrical pulse having duration τP, and which provides sufficient heat energy to cause thermal expansion of the first deflector layer relative to the second deflector layer, resulting in deflection of the cantilevered element to a second position, where τP<½ τB;
• and
• (b) waiting for a time τC before applying a next electrical pulse, where τC>3 τB, so that heat diffuses through the barrier layer to the second deflector layer and the cantilevered element is restored substantially to the first position before next deflecting the cantilevered element.

A liquid drop emitter comprising:

• (a) a chamber, formed in a substrate, filled with a liquid and having a nozzle for emitting drops of the liquid;
• (b) a thermal actuator having a cantilevered element extending a length L from a wall of the chamber and a free end residing in a first position proximate to the nozzle, the cantilevered element including a first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L, a second deflector layer, and a barrier layer constructed of a dielectric material having low thermal conductivity wherein the barrier layer is bonded between the first deflector layer and the second deflector layer;
• and
• (c) a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to cause resistive heating of the first deflector layer, resulting in a thermal expansion of the first deflector layer relative to the second deflector layer and rapid deflection of the cantilevered element, ejecting liquid at the nozzle, followed by restoration of the cantilevered element to the first position as heat diffuses through the barrier layer to the second deflector layer and the cantilevered element reaches a uniform temperature.

A method for operating a liquid drop emitter, said liquid drop emitter comprising a chamber, filled with a liquid, having a nozzle for emitting drops of the liquid, a thermal actuator having a cantilevered element extending a length L from a wall of the chamber and a free end residing in a first position proximate to the nozzle for exerting pressure on the liquid at the nozzle, the cantilevered element including a first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion patterned to have a first uniform resistor portion extending a length LH from the base element, wherein 0.3L≦LH1≦0.7L, a second deflector layer, and a barrier layer constructed of a dielectric material having low thermal conductivity wherein the barrier layer is bonded between the first deflector layer and the second deflector layer;

• and a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to heat the first deflector layer, the method for operating comprising:
• (a) applying to the first pair of electrodes an electrical pulse of duration τP, and which provides sufficient heat energy to cause thermal expansion of the first deflector layer relative to the second deflector layer resulting in liquid drop emission, where τP<½ τB;
• and
• (b) waiting for a time τC before applying a next electrical pulse, where τC>3 τB, so that heat diffuses through the barrier layer to the second deflector layer and the free end is restored substantially to the first position before next emitting liquid drops.

A thermal actuator for a micro-electromechanical device comprising:

• (a) a base element;
• (b) a cantilevered element extending a length L from the base element residing in a first position, the cantilevered element including 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 patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L, and a second deflector layer constructed of a second electrically resistive material having a large coefficient of thermal expansion and patterned to have a second uniform resistor portion extending a length LH2 from the base element, wherein 0.3L≦LH2≦0.7L, wherein the barrier layer is bonded between the first and second deflector layers;
• (c) a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to cause resistive heating of the first deflector layer, resulting in a thermal expansion of the first deflector layer relative to the second deflector layer;
• (d) a second pair of electrodes connected to the second uniform resistor portion to apply an electrical pulse to cause resistive heating of the second deflector layer, resulting in a thermal expansion of the second deflector layer relative to the first deflector layer, wherein application of an electrical pulse to either the first pair or the second pair of electrodes causes deflection of the cantilevered element away from the first position to a second position, followed by restoration of the cantilevered element to the first position as heat diffuses through the barrier layer and the cantilevered element reaches a uniform temperature.

A method for operating a thermal actuator, said thermal actuator comprising a base element, a cantilevered element extending a length L from the base element and residing in a first position, the cantilevered element including a barrier layer, having a heat transfer time constant of τB, bonded between a first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion and patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L, and a second deflector layer constructed of a second electrically resistive material having a large coefficient of thermal expansion and patterned to have a second uniform resistor portion extending a length LH2 from the base element, wherein 0.3L≦LH2≦0.7L;

• a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to heat the first deflector layer;
• and a second pair of electrodes connected to the second uniform resistor portion to apply an electrical pulse to heat the second deflector layer;
• the method for operating comprising:
• (a) applying to the first pair of electrodes a first electrical pulse which provides sufficient heat energy to cause a first deflection of the cantilevered element;
• (b) waiting for a time τW1;
• (c) applying to the second pair of electrodes a second electrical pulse which provides sufficient heat energy to cause a second deflection of the cantilevered element;
• wherein the time τW1 is selected to achieve a predetermined resultant of the first and second deflections.

A liquid drop emitter comprising:

• (a) a chamber, formed in a substrate, filled with a liquid and having a nozzle for emitting drops of the liquid;
• (b) a thermal actuator having a cantilevered element extending a length L from a wall of the chamber and a free end residing in a first position proximate to the nozzle, the cantilevered element including 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 patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L, and a second deflector layer constructed of a second electrically resistive material having a large coefficient of thermal expansion and patterned to have a second uniform resistor portion extending a length LH2 from the base element, wherein 0.3L≦LH2≦0.7L, wherein the barrier layer is bonded between the first and second deflector layers;
• (c) a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to cause resistive heating of the first deflector layer, resulting in a thermal expansion of the first deflector layer relative to the second deflector layer;
• (d) a second pair of electrodes connected to the second unifier resistor portion to apply an electrical pulse to cause resistive heating of the second deflector layer, resulting in a thermal expansion of the second deflector layer relative to the first deflector layer, wherein application of electrical pulses to the first and second pairs of electrodes causes rapid deflection of the cantilevered element, ejecting liquid at the nozzle, followed by restoration of the cantilevered element to the first position as heat diffuses through the barrier layer and the cantilevered element reaches a uniform temperature.

A method for operating a liquid drop emitter, said liquid drop emitter comprising a chamber, filled with a liquid, having a nozzle for emitting drops of the liquid;

• a thermal actuator having a cantilevered element extending a length L from a wall of the chamber and a free end residing in a first position proximate to the nozzle for exerting pressure on the liquid at the nozzle, the cantilevered element including a barrier layer, having a heat transfer time constant of τB, bonded between a first deflector layer constructed of a first electrically resistive material having a large coefficient of thermal expansion and patterned to have a first uniform resistor portion extending a length LH1 from the base element, wherein 0.3L≦LH1≦0.7L, and a second deflector layer constructed of a second electrically resistive material having a large coefficient of thermal expansion and patterned to have a second uniform resistor portion extending a length LH2 from the base element, wherein 0.3L≦LH2≦0.7L;
• a first pair of electrodes connected to the first uniform resistor portion to apply an electrical pulse to heat the first deflector layer;
• and a second pair of electrodes connected to the second uniform resistor portion to apply an electrical pulse to heat the second deflector layer;
• the method for operating comprising:
• (a) applying to the first pair of electrodes a first electrical pulse which provides sufficient heat energy to cause a first deflection of the cantilevered element;
• (b) waiting for a time τW1;
• (c) applying to the second pair of electrodes a second electrical pulse which provides sufficient heat energy to cause a second deflection of the cantilevered element;
• wherein the time τW1 is selected to achieve a predetermined motion of the thermal actuator resulting in liquid drop emission.