Micro-electromechanical liquid ejection device

1. A micro-electromechanical liquid ejection device that comprises

a wafer substrate that incorporates drive circuitry and that defines a liquid inlet;

a nozzle chamber structure that is positioned on the wafer substrate and defines a nozzle chamber in fluid communication with the liquid inlet and a liquid ejection port in fluid communication with the nozzle chamber;

an actuator that is connected to the drive circuitry to be reciprocally displaceable with respect to the substrate on receipt of an electrical signal from the drive circuitry;

a liquid displacement member positioned in the nozzle chamber and displaceable to eject liquid from the fluid ejection port; and

a sealing structure interconnecting the liquid displacement member and the actuator, the sealing structure and the nozzle chamber structure being configured so that the liquid generates fluidic seals between the nozzle chamber structure and the sealing structure to inhibit the egress of liquid from the nozzle chamber during operation.

2. A micro-electromechanical liquid ejection device as claimed in claim 1 , in which the actuator is an elongate thermal actuator that is fast, at one end, with the wafer substrate, while the other end is fast with the sealing structure.

3. A micro-electromechanical liquid ejection device as claimed in claim 2 , in which the thermal actuator has a pair of activating members of a material having a coefficient of thermal expansion which is such that the material is capable of performing work when heated, one of the activating members being connected to the drive circuitry layer to be heated on receipt of a signal from the drive circuitry layer so that said one of the activating members expands to a greater extent than the remaining activating member, resulting in displacement of an actuator arm, a gap being defined between the activating members.

4. A micro-electromechanical liquid ejection device as claimed in claim 3 , in which a strut is interposed between the activating members and is fast with the activating members to reinforce the actuator.

5. A micro-electromechanical liquid ejection device as claimed in claim 3 , in which a heat sink is operatively arranged relative to said one of the activating members, intermediate the ends of the actuator, to reduce excessive heat build up in said one of the activating members.

6. A micro-electromechanical liquid ejection device as claimed in claim 3 , in which the nozzle chamber structure includes a cylindrical sidewall and a roof positioned on the sidewall, the sealing structure defining a part of said sidewall and having a generally I-shaped profile when viewed in plan, with an arcuate end portion, a leg portion and a rectangular base portion, the leg portion interposed between the end portion and the base portion, when viewed in plan.

7. A micro-electromechanical liquid ejection device as claimed in claim 6 , in which the roof defines an arcuate slot that accommodates the end portion and the sidewall defines an opening into the arcuate slot, the opening being dimensioned to accommodate the leg portion.