Method of fabricating a micro-electromechanical actuating mechanism
View Patent ↗A method of fabricating a micro-electromechanical actuating mechanism on a wafer substrate includes the step of carrying out a CMOS fabrication process on the wafer to form transistor control and drive circuitry. Sacrificial material is deposited on the transistor control and drive circuitry. The sacrificial material is etched to provide connection access to the drive circuitry. A MEMS fabrication process is carried out on the layer of sacrificial material to form a micro-electromechanical actuator connected to the drive circuitry and responsive to electrical signals from the drive circuitry. The sacrificial material is removed to free the actuator. The steps of carrying out the CMOS and MEMS fabrication processes are such that the transistor circuitry is interposed between the actuator and the wafer substrate.
1. A method of fabricating a micro-electromechanical actuating mechanism on a wafer substrate, the method comprising the steps of:
carrying out a CMOS fabrication process on the wafer to form transistor control and drive circuitry;
depositing sacrificial material on the transistor control and drive circuitry;
etching the sacrificial material to provide connection access to the drive circuitry;
carrying out a MEMS fabrication process on the layer of sacrificial material to form a micro-electromechanical actuator connected to the drive circuitry and responsive to electrical signals from the drive circuitry; and
removing the sacrificial material to free the micro-electromechanical actuator, wherein
the steps of carrying out the CMOS and MEMS fabrication processes are such that the transistor circuitry is interposed between the actuator and the wafer substrate.
2. A method as claimed in claim 1 , in which the step of carrying out the MEMS fabrication process is such that the micro-electromechanical actuator is elongate, with one end anchored to the substrate.
3. A method as claimed in claim 2 , in which the step of carrying out the CMOS fabrication process includes the step of forming traces for the transistor circuitry such that the traces include a series of portions that extend transversely with respect to the micro-electromechanical actuator.
4. A method as claimed in claim 3 , in which the step of carrying out the MEMS fabrication process includes the step of forming actuator layers on the sacrificial material such that one of the actuator layers defines a series of corrugations that correspond with the series of transversely extending portions of the heater layer.
5. A method as claimed in claim 4 , in which the step of forming the actuator layers includes the step of forming said one of the actuator layers in the form of a resistive heating circuit of a conductive material in electrical contact with the drive transistor circuitry to be heated on receipt of an electrical signal from the drive transistor circuitry.
6. A method as claimed in claim 5 , in which the resistive heating circuit is formed with a conductive material having a coefficient of thermal expansion sufficient to result in expansion and subsequent contraction of the heating circuit upon heating and subsequent cooling to result in displacement of the micro-electromechanical actuator with respect to the substrate.
7. A method as claimed in claim 6 , in which the step of forming said resistive heating circuit incorporates the steps of forming a fluid ejection paddle such that said one of the actuator layers also defines the fluid ejection paddle, and forming an electrical discontinuity between the fluid ejection paddle and the heating circuit to insulate the fluid ejection paddle.
8. A method as claimed in claim 7 , which includes the step of forming a nozzle chamber structure on the substrate to define a nozzle chamber such that the fluid ejection paddle extends into the nozzle chamber and the actuator extends through a wall of the nozzle chamber structure.