Sensors and Actuators A 190 (2013) 84–89 Contents lists available at SciVerse ScienceDirect Sensors and Actuators A: Physical jo u rn al hom epage: www.elsevier.com/locate/sna Fabrication, assembly, and testing of a MEMS-enabled micro gas compressor for a 4:1 pressure ratio Ryan Lewis ∗ , Collin J. Coolidge, Paul J. Schroeder, Victor M. Bright, Y.C. Lee Department of Mechanical Engineering, University of Colorado at Boulder, 427 UCB, Boulder, CO, USA a r t i c l e i n f o Article history: Received 19 September 2012 Received in revised form 29 October 2012 Accepted 4 November 2012 Available online 22 November 2012 Keywords: Gas compressor Micro-valve Piezoelectric MEMS a b s t r a c t This study describes the fabrication, assembly, and testing of a micro gas compressor. The compressor is formed by MEMS-based check valves coupled to a Kapton membrane driven by a mechanically amplified piezoelectric actuator. The valves are surface machined on a silicon substrate using polyimide as the structural material and copper as the sacrificial material. This design allows valves with low leak rates, low compressor dead volume, and the high compressible volume required to generate the pressure levels required of numerous applications including cryogenic cooling. The assembled compressor is tested with voltages over the range of 25–180 V and frequencies over the range of 25–700 Hz. A maximum pressure ratio of 4.3:1 is found when the actuator provides a maximum displacement of 156 m, while the maximum flow-rate through the compressor of 51 standard cubic cm per minute (sccm) is observed when the compressor is operating at its resonant frequency. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Numerous micro systems benefit from micro gas compressors, including micro gas chromatography systems [1,2], micro reactors with gas-phase reactants [3], micro fuel cells [4,5], and micro refrig- eration [6]. Of particular interest are micro vapor-compression refrigeration systems which require compressors to increase the pressure of the refrigerant [7], as do Joule–Thomson cryogenic systems [8]. Several groups have demonstrated micro-scale heat exchangers and expansion valves, but have used considerably larger compression systems [9–12]. There have been a number of studies investigating micropumps to compress a gas-phase fluid. Some of the more successful compressors operate with an actu- ated membrane and check valves [13–15]. Peristaltic pumps and valveless pumps have also been investigated for use as a com- pressor [16,17]. However, these pumps are unable to generate the pressures required for refrigeration and cryogenic systems. A maximum compression pressure ratio of 1.2:1 has been reported by Yoon et al. [15], but a minimum pressure ratio of 4:1 is required for a number of mixed-refrigerant Joule–Thomson sys- tems [18,19]. Previous studies on micro compressors have generated low pressures due to a low ratio of swept volume to dead volume. In an isothermal system compressing a fixed mass of an ideal gas, the ratio of the final pressure to the initial pressure can be determined ∗ Corresponding author. Tel.: +1 5094383587. E-mail address: rjlewis@colorado.edu (R. Lewis). by the ideal gas law to be the ratio of the initial volume to the final volume: P f /P i = V i /V f . This final volume is considered “dead” volume. A well designed compressor will therefore have a minimized dead volume while maintaining a high swept volume. The microcompressor used in this study is formed by MEMS- based check valves coupled to a Kapton membrane driven by a mechanically amplified piezoelectric actuator, shown in Fig. 1. Pressure ratios above 4:1 have been repeatedly demonstrated with this device. Pressures, flow-rates, and power-draw are mea- sured as a function of actuator voltage and frequency. Further modifications to the assembly are suggested to improve the performance. 2. Fabrication and assembly 2.1. Design The general design of the micro compressor is shown in Fig. 1. It consists of a pair of MEMS based check valves, epoxy-bonded to a stainless steel valve substrate. A metalized Kapton mem- brane is pressed onto the substrate by a clamping fixture. Sealing between the membrane and substrate is facilitated by an o-ring recessed in the substrate, such that it does not contribute signif- icant dead volume upon sealing. The membrane is soldered to a copper “button” which connects to a mechanically amplified piezoelectric actuator. The actuator provides the high stroke length and force necessitated to generate the required high operating pressures. 0924-4247/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2012.11.008