肖振華111.txt

1、----------------------- Page 1-----------------------Sensors and Actuators A 136 (2007) 374–384 Development of various designs of low-power, MEMS valves for fluidic applications A.M. Cardenas-Valencia a, , J. Dlutowskia

2、,b, J. ?Bumgarnera, C. Munoz a,b, W. Wanga, R. Popuria, L. Langebrakeaa Center for Ocean technology, University of South Florida, 140 Seventh Ave. S. St Petersburg FL 33701, United States b Department of Electrical En

3、gineering, University of South Florida, 4202 E. Fowler Ave, Tampa FL 33620, United States Received 11 July 2006; received in revised form 28 November 2006; accepted 19 December 2006 Available online 22 December 2006 A

4、bstract Automated, controlled fluid delivery is an important operation in micro-total analysis systems (TAS). Actuated micro-valves have been proposed to separate a pressurized fluid from the channel to

5、 be filled. This scheme greatly reduced the energy required to move the fluid. The design, micro-fabrication and performance of arrays of single-use valve, which constitute an integral part of this actuation mechanism

6、, is presented. The addressable constituent of the valve is a thin metallic ohmic resistor, whose design dictates the actuation voltage. The resistor is patterned on a silicon nitride membrane that constitutes the flo

7、w barrier, which stands on a silicon wafer. Rapid heating via an electric pulse induces thermal stresses in the membrane/resistor, which in turn breaks the membrane opening the valves. The chosen processing steps allow

8、 for wafer-level device fabrication using standard MEMS processing tools. Different size membranes with various thicknesses (1, 2 and 3 m) are tested. Valves that withstand a pressure differential of up to 5 bar (3 mm

9、 ×3 mm, 3 m-thick silicon nitride membranes) were chosen for the study. Investigated valves were activated with a potentials ranging between 14 and 140 V and required activation energies from tens to hundreds of

10、milliJoules. © 2007 Elsevier B.V. All rights reserved. Keywords: Thermally actuated; Single-use; Micro-valves 1. Introduction Many works in literat

11、ure exemplify fluidic delivery mecha- nisms, and the references herein are a small sample [7–14]. Pneu- Micro-fluidics has been included in various analytical matically or inertiallly driven fluid

12、ic devices are preferred over schemes that incorporate the well-known advantages of micro- electrokinetic mechanisms due to their capacity to provide a scale transduction. A basic fluidic op

13、eration important in TAS wider range of flow rates [10–14]. CD-styled platforms, based and Lab-on-a-chip applications is the controlled delivery of on centrifugal forced actuation,

14、 are a classical example of micro- minute fluid amounts. The purposes behind hermetic fluid stor- fluidic schemes [11]. Volume-expanding materials are another age and its on-demand delivery, even as

15、 a single-use operation, and fabricate micro-valves that require different power specifi- of the energy required for actuation to fractions of a Joule is cations, facilitating its potentia

16、l integration in portable sensors, reported in thermally activated “burst-plug” valves by Mueller are shown. et al. [27,28]. The design proposed here, also based on thermally induced stresses, differs

17、 from other works in that the valve is 2.2. Theoretical background and resistor designs formed by a membrane on which a thin resistor is patterned (Fig. 1a). This design offers versatilit

18、y, as the valves can be If single-use valves (an array is shown in Fig. 1) are to be used fabricated with various dimensions (leading to valves capable in a stored-pneumatic-energy fluidic

19、 mechanism, two impor- of various operating conditions) and on different wafers than tant issues must be considered. On one hand a mechanically those where the micro-channels and/or other f

20、luidic components strong membrane to contain the pressurized fluid is desirable. are located. Hoses and fluidic ports, popular in micro-fluidics The stronger the membrane, the higher

21、the pressure differen- research and development, easily interconnect devices, as shown tial it can withstand, and the faster the liquid filling of the in Fig. 1b. Well characterized and comm

22、on processing steps were desired channel/reservoir. On the other hand, the membrane selected with the aim of achieving high yields. If implemented as has to be reliably broken with s

23、mall amounts of energy and the shown in Fig. 1b, the actuation energy requirements are dictated breakage time lag must be small. In this report, the maximum by the consumed power of the valving mechanism.

24、 This work pressure that several size membranes can withstand is exper- reports on the micro-valve fabrication and empirically studies imentally determined. Phenomenological m

25、echanical models, designs requiring low activation energies. solved generally using numerical techniques, are well docu- mented in literature [34,35]. A simple descriptive mo

26、del is used 2. Valves designs: practical and theoretical herein to quantify the maximum pressure differential that the considerations

27、 membranes can withstand. The descriptive model is valid for a membrane with large planar dimensions in comparison with its 2.1. On the selection of materials for micro-valve

28、 thickness (which is the case herein) and can be used to relate fabrication the required breakage pressure and the membrane dimensions [36]. A force

29、 balance can be written, when the pressures fac- Thin resistors deposited on silicon nitride have been realized ing each face of the membrane changes, as an equation of the for various sensing applications

30、(gas and pressure transducers) form, Fig. 1. (a) Schematic illustrating the silicon membrane and a patterned resistor that constitute the single-use valves described here. (b) Conceptualization on the