We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

This review gives a brief overview of microvalves, and focuses on the actuation mechanisms and their applications. One of the stumbling blocks for successful miniaturization and commercialization of fully integrated microfluidic systems was the development of reliable microvalves. Applications of the microvalves include flow regulation, on/off switching and sealing of liquids, gases or vacuums. Microvalves have been developed in the form of active or passive microvalves employing mechanical, non-mechanical and external systems. Even though great progress has been made during the last 20 years, there is plenty of room for further improving the performance of existing microvalves.

http://iopscience.iop.org/article/10.1088/0960-1317/16/5/R01/pdf

A review of microvalves

Microfluidics has emerged from the MEMS-technology as an important research field and a promising market. We give an overview on one of the most important microfluidic components: the micropump. In the last decade, various micropumps have been developed. There are only a few review papers on microfluidic devices and none of them were dedicated only to micropumps. This review paper outlines systematically the pump principles and their realization with MEMS-technology. Comparisons regarding pump size, flow rate, and backpressure will help readers to decide their proper design before starting a microfluidics project. Different pump principles are compared graphically and discussed in terms of their advantages and disadvantages for particular applications

MEMS-Micropumps: A Review

This paper briefly overviews progress on the development of MEMS-based micropumps and their applications in drug delivery and other biomedical applications such as micrototal analysis systems (μTAS) or lab-on-a-chip and point of care testing systems (POCT). The focus of the review is to present key features of micropumps such as actuation methods, working principles, construction, fabrication methods, performance parameters and their medical applications. Micropumps have been categorized as mechanical or non-mechanical based on the method by which actuation energy is obtained to drive fluid flow. The survey attempts to provide a comprehensive reference for researchers working on design and development of MEMS-based micropumps and a source for those outside the field who wish to select the best available micropump for a specific drug delivery or biomedical application. Micropumps for transdermal insulin delivery, artificial sphincter prosthesis, antithrombogenic micropumps for blood transportation, micropump for injection of glucose for diabetes patients and administration of neurotransmitters to neurons and micropumps for chemical and biological sensing have been reported. Various performance parameters such as flow rate, pressure generated and size of the micropump have been compared to facilitate selection of appropriate micropump for a particular application. Electrowetting, electrochemical and ion conductive polymer film (ICPF) actuator micropumps appear to be the most promising ones which provide adequate flow rates at very low applied voltage. Electroosmotic micropumps consume high voltages but exhibit high pressures and are intended for applications where compactness in terms of small size is required along with high-pressure generation. Bimetallic and electrostatic micropumps are smaller in size but exhibit high self-pumping frequency and further research on their design could improve their performance. Micropumps based on piezoelectric actuation require relatively high-applied voltage but exhibit high flow rates and have grown to be the dominant type of micropumps in drug delivery systems and other biomedical applications. Although a lot of progress has been made in micropump research and performance of micropumps has been continuously increasing, there is still a need to incorporate various categories of micropumps in practical drug delivery and biomedical devices and this will continue to provide a substantial stimulus for micropump research and development in future.

https://www.nectec.or.th/mems/download/MEMS-based%20Micropumps%20in%20Drug.pdf

MEMS-based micropumps in drug delivery and biomedical applications

Electroosmotic flow (EOF) micropumps which use electroosmosis to transport liquids have been fabricated and used to achieve pressures in excess of 20 atm and flow rates of 3.6 μl/min for 2 kV applied potentials. These pumps use deionized water as working fluids in order to reduce the ion current of the pump during operation and increase thermodynamic efficiency. EOF pumps are fabricated by packing the 3.5 μm diameter non-porous silica particles into 500–700 μm diameter fused-silica capillaries and by using a silicate frit fabrication process to hold the particles in place. The devices have no moving parts and can operate as both open (high flow rate) and closed (high pressure) systems. Pressure versus flow rate performance data are presented and combined with measurements of physical dimensions, dry and wet weight, and ion current to calculate the pump structure porosity, tortuosity, effective pore radius, and zeta potential.

Fabrication and characterization of electroosmotic micropumps

A piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed.

/pdf/a-piezoelectric-microvalve-for-compact-high-frequency-high-2unkr4h0s8.pdf

A piezoelectric microvalve for compact high-frequency, high-differential pressure hydraulic micropumping systems

The fabrication of an active MEMS microvalve driven by integrated bulk single crystal piezoelectric actuators is reported. The valve has a nine-layer structure composed of glass, silicon, and silicon on insulator (SOI) layers assembled by wafer-level fusion bonding and anodic bonding, as well as die-level anodic bonding and eutectic bonding. Valve head strokes as large as 20 μm were realized through hydraulic amplification of the small stroke of the piezoelectric actuator. A flow rate of 0.21 ml/s was obtained at 1 kHz. The fabrication, bonding and assembly process, as well as some test results are described.

Fabrication of a high frequency piezoelectric microvalve

/pdf/a-high-frequency-high-flow-rate-piezoelectrically-driven-3d8gzrcjso.pdf

A High Frequency High Flow Rate Piezoelectrically Driven MEMS Micropump

Towards the development of novel class of miniature transducers with very high specific power, a high frequency and high flow rate hydraulic micro-pump with passive check valves was fabricated and tested. The micro-pump features a small piezoelectric (PZT-5H/PZN-PT) cylinder integrated into micromachined silicon and pyrex chips. The piezoelectric cylinder bonded to a thick circular disk serves as the drive element in the pump chamber, and two axisymmetric silicon membranes with hollow annular bosses serve as system check valves. Using silicone oil as the working fluid, the performance of the micro-pump was tested by varying voltages from 0 to 1600 V and frequencies from 1 kHz to 12 kHz. The micro-pump with PZT-5H element achieved a high flow rate of 2.5 ml/min at 1200 V and 4.5 kHz.

Design, fabrication, and testing of a piezoelectrically driven high flow rate micro-pump

This paper presents a microfabricated electroquasistatic (EQS) induction turbine-generator that has generated net electric power. A maximum power output of 192 /spl mu/W was achieved under driven excitation. We believe that this is the first report of electric power generation by an EQS induction machine of any scale found in the open literature. This paper also presents self-excited operation in which the induction generator self-resonates and generates power without the use of any external drive electronics. The generator comprises five silicon layers, fusion bonded together at 700/spl deg/C. The stator is a platinum electrode structure formed on a thick (20 /spl mu/m) recessed oxide island. The rotor is a thin film of lightly doped polysilicon also residing on an oxide island, (10 /spl mu/m) thick. This paper also presents a generalized state-space model for an EQS induction machine that takes into account the machine and its external electronics and parasitics. This model correlates well with measured performance and was used to find the optimal drive conditions for all driven experiments.

http://ieeexplore.ieee.org/iel5/9868/31227/01454004.pdf

J.L. Steyn

Papers

A piezoelectric microvalve for compact high-frequency, high-differential pressure hydraulic micropumping systems

Fabrication of a high frequency piezoelectric microvalve

A High Frequency High Flow Rate Piezoelectrically Driven MEMS Micropump

Design, fabrication, and testing of a piezoelectrically driven high flow rate micro-pump

Generating electric power with a MEMS electroquasistatic induction turbine-generator