Electro-Thermal Analysis of In-Plane Micropump

This paper describes the modeling for a packaged in-plane micropump developed at the Automation and Robotics Research Institute, The University of Texas, Arlington, TX. Amongst the family of micro-electro-mechanical system (MEMS) devices, thermal actuators are important owing to their capability to deliver a large force and displacement. Due to fabrication and cost-savings advantages, these actuators are now commonly used in several applications, such as optical-communication switches, micro-assembly, and micro-positioners. The proposed micropump design is based on these actuators fabricated by a one-step deep reactive ion etching process and packaged for protection and appropriate thermal dissipation. In the current ongoing research, the thermal actuator forms an integral part of an in-plane micropump. The flow rate is controlled by the variations in actuator displacement and corresponding force generated. Flow rates of several micro-liters per minute can be obtained making this pump suitable for drug delivery applications. Actuation is caused by application of voltage and resulting joule heating effect of the MEMS chevron beams. This results in displacement of the beams (actuator) which is proportional to the difference in temperature. Some of the parameters governing the displacement include the applied voltage, resistivity of the device, substrate thickness, and air gap between the device and the substrate. In this paper, the proposed micro-pump was analyzed for its thermal performance, pumping force, and the corresponding flow rate. The analysis was performed at device, die, and package levels. Thermal analysis showed that there exists a linear relationship between the applied voltage and the resulting temperature. Maximum temperature was always noted at the center of the chevron beams. The analysis also showed that force generated by the thermal actuators mainly depends on the average temperature of the chevron beams. Maximum force of 3.73 mN was noted for the packaged micropump at 23 V. This corresponded to an average beam temperature of 453°C and a flow rate of 11.2 μl/min. Performance assessment of the pump showed that for every 5 kPa increase in backpressure, flow rate reduced approximately by 5%.