A fully polymeric micropump with piezoelectric actuator

doi:10.1016/S0925-4005(03)00521-5

Sensors and Actuators B: Chemical

Volume 97, Issue 1, 1 January 2004, Pages 137-143

https://doi.org/10.1016/S0925-4005(03)00521-5 Get rights and content

Abstract

This paper presents a new concept of designing and fabricating polymeric micropumps. The micro pump is made of SU-8 photoresist and polymethylmethacrylate (PMMA). The key elements of the micropump are the micro check valves, which are fabricated in a 100-μm-thick SU-8 film. The SU-8 part is designed as a disc with 10-mm diameter. The check valves are 1-mm discs suspended on a compliant orthoplanar spring with four arms. The cross section of the spring beam has a dimension of $100 μm ×100$ μm. The pump is designed as a stack of different layers, which are made of PMMA and SU-8. In contrast to their silicon counterparts, the low spring constant of the SU-8 check valves allows the use of relatively low drive voltages on the order of several 10 V for the piezodisc, which works as the pump’s actuator. Pump rates up to 1 ml/min and back pressures up to 200 mm water have been achieved. The pump design shows the feasibility of our current effort to make microfluidic systems based on the lamination of different polymeric materials.

Introduction

The development of pumping devices in microscale is a part of the emerging research field of microfluidics [1]. Besides stand-alone micropumps, simple pump designs are required for integration in miniaturized chemical analyzers, which are often called micro total analysis systems (μTAS) or lab on a chip (LOC). The trend of a disposable system in form of a plastic test cartridge leads to the need of simple polymeric micropumps, which can be easily implemented in the fabrication process of the test cartridge. Furthermore, low-voltage and low-power actuating schemes for the pump are needed for the use in hand-held devices, which are usually powered by batteries.

The development of micropumps has a history of more than two decades. Generally, micropumps can be categorized as mechanical pumps and nonmechnical pumps [1], [2]. While mechanical pumps apply conventional concepts in microscale, nonmechanical pumps utilize effects which are dominant in microscales such as surface tension and electrokinetics. Since the size of the above mentioned test cartridges is in the mesoscale, mechanical pumps are still relevant. References [1], [2] give detailed description of different micropump concepts.

With the need of polymeric microdevices, polymer-based micromachining techniques have been established recently as new alternatives in microtechnology. The basic polymer-based micromachining techniques are thick resist lithography, polymeric surface micromachining, soft lithography, micro stereolithography and micromolding [1]. The advantage of polymer-based micromachining is the possible use of different polymeric materials, which may offer μTAS good biocompatibility and chemical resistance.

A significant advantage of polymers over silicon is their relatively low Young’s modulus, which is 50-100 times smaller than that of silicon. Thus, check valves made of polymers require less pressure for operating. Furthermore, the softer polymeric material offers much better sealing characteristics. A number of works on polymeric check valves was reported. Check valves were fabricated in polyimide [3], [4], [5], [6], polyester [7], parylene [8], and silicone rubber [9]. In some cases the check valves are simply made of manually punched polymer film [7], [9]. SU-8 is a negative thick-film photoresist, which has been widely used for making microchannels [1]. In this paper, we report the first SU-8 check valves with movable structures. The structures are fabricated and released with the so-called polymeric surface micromachining technique [1], which can make freely moveable polymeric microstructures. More importantly, we demonstrate in this paper the layered concept for making microfluidic systems. This concept lays the foundation for the lamination technique, which is currently developed by our research group.

Section snippets

Micropump design

Fig. 1 depicts the assembly concept of our micropump. The pump consists of six layers of different materials. The first polymethylmethacrylate (PMMA) plate has an opening at the center for the piezodisc. This plate is used for fixing the piezodisc. The piezodisc works as both actuator and pump membrane. The characteristics of the piezodisc were described previously in [10]. The pump chamber is defined by the piezodisc and a second PMMA plate, which has two access holes for inlet and outlet. The

Design

Fig. 3 depicts the most important geometry parameters of the SU-8 disc. The disc is 100-μm thick and has a diameter of 10 mm. The check valve consists of a 1-mm circular plate suspended on four folded springs. The spring design is called the compliant orthoplanar spring [11]. This design assures that the valve plate is displaced in parallel to the disc surface, Fig. 4. The valve springs are folded beams with a cross section of $100 μm ×100$ μm. The circular hole next to the spring structures works as

Characterization results

The micro check valve was first characterized. A large water reservoir with variable surface heights was used for adjusting the pressure across the micro check valve. The large reservoir ensures a constant height and a constant inlet pressure during the measurement. The pressure was measured with a pressure sensor (Honeywell 22PC-Series, ±1 psi) which was calibrated for a pressure range from 0 to 6000 Pa. The flow rate was measured by determining the velocity of the water/air interface in the

Conclusion and future works

We have designed, fabricated and characterized a fully polymeric micropump with piezoelectric actuator. The most important parts of the pump are the two micro check valves, which are fabricated in a 100-μm-thick SU-8 film using a one-mask lithography process. The valves feature the compliant orthoplanar spring design. The other parts such as pump chamber and housing are machined using conventional cutting and milling techniques. The pump achieves flow rates and back pressure up to 1 ml/min and

Acknowledgements

This work was supported by the academic research fund of the ministry of education Singapore, contract number RG11/02. The authors thank the MEMS-lab at the Singapore Polytechnic for their collaboration in fabricating the SU-8 check valves.

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Nam-Trung Nguyen was born in Hanoi, Vietnam, in 1970. He received his Dip.-Ing. And Dr. Ing. degrees from Chemnitz University of Technology, Germany, in 1993 and 1997, respectively. In 1998, he worked as a postdoctoral research engineer in the Berkeley Sensor and Actuator center (UC Berkeley, USA). Currently he is an assistant professor with the School of Mechanical and Production Engineering of the Nanyang Technological University in Singapore. His research is focused on microfluidics and instrumentation for biomedical applications. He published a number of research papers on microfluidics. His recent book “Fundamentals and Applications of Microfluidics” co-authored with S. Wereley was published in October 2002.

Thai-Quang Truong was born in Vietnam in 1972. He received the MSc in electronics engineering in 2001 from Nanyang Technological University, Singapore. He is currently working towards the PhD degree in microtechnology at the School of Mechanical and Production Engineering of the Nanyang Technological University in Singapore.

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A fully polymeric micropump with piezoelectric actuator

Abstract

Introduction

Section snippets

Micropump design

Design

Characterization results

Conclusion and future works

Acknowledgements

Sens. Actuators A

Sens. Actuators B

Sens. Actuators A

Sens. Actuators A

MEMS–micropumps: a review

ASME Trans. J. Fluids Eng.

Active valves and pumps for microfluidics

J. Micromechanics Microeng.