Micro-electromechanical fluid ejecting device that incorporates a covering formation for a micro-electromechanical actuator

1. A micro-electromechanical fluid ejection device that comprises

a substrate that incorporates drive circuitry and defines a fluid inlet channel;

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

a micro-electromechanical actuator that is positioned on the substrate and is electrically connected to the drive circuitry to be displaced relative to the substrate on receipt of an electrical current from the drive circuitry;

a fluid ejecting member that is positioned in the nozzle chamber and is connected to the actuator to eject fluid from the ink ejection port on displacement of the actuator; and

a covering formation that is positioned on the substrate and is configured to enclose the micro-electromechanical actuator.

2. A micro-electromechanical fluid ejection device as claimed in claim 1 , in which the covering formation includes sidewalls that extend from the substrate and a roof wall that spans the substrate.

3. A micro-electromechanical fluid ejection device as claimed in claim 2 , in which the actuator is elongate and has a fixed end that is connected to the substrate so that the actuator can receive an electrical signal from the drive circuitry and a movable end, the actuator being configured so that the movable end is displaced relative to the substrate on receipt of the electrical signal.

4. A micro-electromechanical fluid ejection device as claimed in claim 3 , in which a motion-transmitting structure is fast with the movable end of the actuator, the motion-transmitting structure being connected to the fluid ejecting member so that movement of the actuator is translated to the fluid ejecting member, the motion-transmitting structure defining part of the roof wall and spaced from a remaining part of the roof wall to allow for movement of the motion-transmitting structure.

5. A micro-electromechanical fluid ejection device as claimed in claim 4 , in which the roof wall defines a cover that spans the walls to cover the elongate actuator, the motion-transmitting structure being shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate, an opening being defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.

6. A micro-electromechanical fluid ejection device as claimed in claim 4 , in which the motion-transmitting structure defines a lever mechanism and has a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation, an effort formation being connected between the movable end of the actuator and the lever arm formation and a load formation being connected between the lever arm formation and the fluid ejecting member.

7. A micro-electromechanical fluid ejection device as claimed in claim 6 , in which the lever arm formation, the cover and the walls define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.

8. A micro-electromechanical fluid ejection device as claimed in claim 3 , in which the actuator includes at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work, the actuator arm having an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the electrical signal from the drive circuitry layer and subsequently cooled on termination of the signal, and a passive portion which is insulated from the drive circuitry layer, the active and passive portions being positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable end of the actuator.