Thermal bend actuator comprising passive element having negative thermal expansion

1. A thermal bend actuator comprising:

a first active element for connection to drive circuitry; and

a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator,

wherein the second element is comprised of a material having negative thermal expansion.

2. The thermal bend actuator of claim 1 , wherein said second element is comprised of a material having a cubic structure.

3. The thermal bend actuator of claim 2 , wherein said second element is comprised of a material of formula: AM 2 O 8 , wherein:

A=Zr or Hf; and

M=Mo or W.

4. The thermal bend actuator of claim 1 , wherein said second element is comprised of cubic zirconium tungstate.

5. The thermal bend actuator of claim 1 , wherein said first element is comprised of a material having positive thermal expansion.

6. The thermal bend actuator of claim 1 , wherein said first element is comprised of a metal nitride, a mixed metal nitride or a metal alloy.

7. The thermal bend actuator of claim 1 , wherein said first and second elements are cantilever beams.

8. The thermal bend actuator of claim 7 , wherein the first beam is fused or bonded to the second beam along a longitudinal axis thereof.

9. A MEMS device comprising a thermal bend actuator according to claim 1 .

10. An inkjet nozzle assembly comprising:

a nozzle chamber having a nozzle opening and an ink inlet; and

a thermal bend actuator for ejecting ink through the nozzle opening, said actuator comprising:

a first active beam for connection to drive circuitry; and

a second passive beam mechanically cooperating with the first beam, such that when a current is passed through the first beam, the first beam expands relative to the second beam, resulting in bending of the actuator,

wherein the second beam is comprised of a material having negative thermal expansion.

11. The inkjet nozzle assembly of claim 10 , wherein the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.

12. The inkjet nozzle assembly of claim 11 , wherein the moving portion comprises the actuator.

13. The inkjet nozzle assembly of claim 12 , wherein the first active beam defines at least 30% of a total area of the roof.

14. The inkjet nozzle assembly of claim 13 , wherein the first active beam defines at least part of an exterior surface of said nozzle chamber.

15. The inkjet nozzle assembly of claim 12 , wherein the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.

16. The inkjet nozzle assembly of claim 10 , wherein said second element is comprised of a material having a cubic structure.

17. The inkjet nozzle assembly of claim 16 , wherein said second element is comprised of a material of formula: AM 2 O 8 , wherein:

A=Zr or Hf; and

M=Mo or W.

18. The inkjet nozzle assembly of claim 10 , wherein said second element is comprised of cubic zirconium tungstate.

19. The inkjet nozzle assembly of claim 10 , wherein said first element is comprised of a material having positive thermal expansion.

20. An inkjet printhead comprising a plurality of nozzle assemblies according to claim 10 .