Modeling and fabrication of electrostatically actuated diaphragms for on-chip valving of MEMS-compatible microfluidic systems (original) (raw)
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Sensors and Actuators A: Physical, 2019
New concept of liquid actuator based on a slack deformable metallized membrane. Expectation of an increase of gap/thickness gain (> X100) in output pressure. Full experimental characterization agrees with theory within +/-15%. A novel concept of microfluidic actuator based on a slack metallized film confined between two parallel grid-electrodes separated by a gap is presented. The film is loosely attached such that it can move freely between the two grid-electrodes. Upon voltage application between the metallized film and one grid-electrode, electrostatic attraction tends to press the metallized film on the grid, thus pushing the fluid through the grid. This evolution happens through a film fold travelling across the cell width. Samples using a replication of grid-electrodes manufactured by silicon anisotropic etching have been assembled. An equilibrium theory of operation and an experimental characterization with measurements of exchanged liquid volumes, differential pressures, capacitance and applied voltage are presented, both agreeing within +/-15%. It will be shown that actuators with an active zone of 8mmx45mm and a gap of 0.25 mm can move 100 µl against differential pressures of about 200 Pa with a 100 V power supply at 100 Hz consuming few tens of mW. The only moving part is the deformable film and the actuator is silent when filled with liquids. The new concept also supports an accurate capacitance monitoring of the exchanged volumes. The actuation can be reversible by connecting one or the other grid electrode. This new pumping mechanism has been primarily designed for exchanging a given volume of two insulating fluids of different refractive indices, in order to activate ophthalmic variable eyeglasses for presbyopia correction. Nevertheless, the same concept can be extended to continuous flow pumping.
Playing with actuators in microfluidic systems
In the labs-on-a-chip of the future, flows will be driven though mazes of microchannels and it will be crucial to integrate actuators achieving flow control ; having actuation available on-chip thus seems a condition for producing large palettes of functionnalities, in a way that could bear comparison with microelectronic devices. In the present paper, we work with PDMS microfluidic systems, and the actuators are made by using multi layer soft technology [1,2]. Thus far, these actuators have mostly been used for producing valving and pumping. Here we describe different usages for these actuators : in particular, we use them for perturbing flow patterns rather than just stopping or driving fluids. This gives rise to interesting functionalities, such as mixing, extracting, building concentration gradients and controlling droplet sizes and emission frequencies.
Journal of Micromechanics and Microengineering, 2012
We describe a new class of electrostatic actuators with a compliant electrode made of liquid metal alloy contained by a thin elastomeric membrane. We illustrate the use of such actuators as on-chip microvalves for gas flow control. The microvalve comprises of one fixed electrode spanning the floor and sidewalls of the trapezoidal gas channel and one corresponding flexible electrode suspended across the channel. Details of fabrication and preliminary characterization of on/off and proportional valving are presented.
Electrochemically actuated passive stop–go microvalves for flow control in microfluidic systems
Microelectronic Engineering, 2013
Flow manipulation is a critical expected capacity for integrated microsystems. One way to realize low cost devices is to take advantage of capillary forces for fluid movement. In such systems, flow manipulation should be achieved with easily operated, effortlessly integrated valves. One advantageous method to operate sensors and actuators in microsystems is electrochemistry. Here, the design, fabrication and implementation of low voltage electrochemically actuated passive stop-go microvalves for on-off fluidic manipulations in microfluidic systems are reported. Two closely spaced electrodes (one of which has superhydrophobic surface) were fabricated by screen printing followed by surface structuring in a microchannel. The fabrication of the superhydrophobic surface (water contact angle (CA) 152°) was performed by selective and controlled solvent-etching of a naturally hydrophobic (CA = 105°) screen printed carbon surface. The process increased the roughness and porosity of the surface that caused the superhydrophobic effect. The superhydrophobic surface of the carbon electrode, in addition to functioning as passive stop valve (PSV), facilitates the flow actuation using low applied voltage avoiding observable electrochemical reactions in aqueous solutions. When a low voltage ($1 V) was applied at the carbon electrode against a silver electrode, the flow of such solutions (e.g. 0.01 M phosphate buffer saline solution) that was stopped at the PSV, resumed, crossing the 1 mm pitch of hydrophobic barrier of the PSV in 1 s and reestablishing capillary flow downstream. The low cost and flexibility of fabrication, facile integration and miniaturization, and reproducible performance of such on/off valves make this configuration promising for the development of low cost microfluidic devices for point-of-care diagnostics, food analysis, and environmental monitoring.
A hybrid microfluidic chip with electrowetting functionality using ultraviolet (UV)-curable polymer
Lab on a Chip, 2010
Electrowetting (EW) is widely used in digital microfluidics for the manipulation of drops sandwiched between two parallel plates. In contrast, demonstrations of closed microfluidic channels enhanced with EW functionality are scarce. Here, we report a simple, low-cost method to construct such microchannels enclosed between two glass plates, each of which comprises electrodes and insulating layers. Our method uses soft imprint lithography with thiolene precursors to design the channel geometry. UV exposure is used to seal the chips permanently and a silanization treatment renders all inner channel surfaces hydrophobic. Compared to earlier polydimethylsiloxane-based designs, this method allows us to make microchannels with smaller dimensions (down to 10 microns), lower aspect ratios (down to height/length = 1/10), and symmetric electrodes both on the top and the bottom of the channel. We demonstrate the new capabilities with two examples: (i) EW-enhanced drop generation in a flow focusing geometry allows precise and continuous control on drop diameter in the range of ≈ 1-15 microns while maintaining monodispersity; (ii) EW allows tuning of the excess water pressure needed to displace oil in a microchannel, leading tospontaneous imbibition at EW number η > 0.89.
Smart Sensors, Actuators, and MEMS, 2003
In this paper, a concept for a monolithically integrated chemical lab on microchip is presented. It contains an ASIC (Application Specific Integrated Circuit), an interface to the polymer based microfluidic layer and a Pyrex glass cap. The top metal layer of the ASIC is etched off and replaced by a double layer metallization, more suitable to microfluidic and electrophoresis systems. The metallization consists of an approximately 50 nm gold layer and a 10 nm chromium layer, acting as adhesion promoter. A necessary prerequisite is a planarized ASIC topography. SU-8 is used to serve as microfluidic structure because of its excellent aspect ratio. This polymer layer contains reservoirs, channels, mixers and electrokinetic micro pumps. The typical channel cross section is 10 µm • 10 µm. First experimental results on a microfluidic pump, consisting of pairs of interdigitated electrodes on the bottom of the channel and without any moving parts show a flow of up to 50 µm per second for low AC-voltages in the range of 5 V for aqueous fluids. The microfluidic system is irreversibly sealed with a 150 µm thick Pyrex glass plate bonded to the SU-8-layer, supported by oxygen plasma. Due to capillary forces and surfaces properties of the walls the system is self-priming. The technologies for the fabrication of the microfluidic system and the preparation of the interface between the lab layer and the ASIC are presented.
PDMS Microcantilever-Based Flow Sensor Integration for Lab-on-a-Chip
IEEE Sensors Journal, 2013
In this paper, a simple practical method is presented to fabricate a high aspect ratio horizontal polydimethylsiloxane (PDMS) microcantilever-based flow sensor integrated into a microfluidic device. A multilayer soft lithography process is developed to fabricate a thin PDMS layer involving the PDMS microcantilever and the microfluidics network. A three-layer fabrication technique is explored for the integration of the microflow meter. The upper and lower PDMS layers are bonded to the thin layer to release the microcantilever for free deflection. A 3-D finite element analysis is carried out to simulate fluid-structure interaction and estimate cantilever deflection under various flow conditions. The dynamic range of flow rates that is detectable using the flow sensor is assessed by both simulation and experimental methods and compared. Limited by the accuracy of the 1.76-µm resolution of the image acquisition method, the present setup allows for flow rates as low as 35 µL/min to be detected. This is equal to 0.8-µN resolution in equivalent force at the tip. This flow meter can be integrated into any type of microfluidicbased lab-on-a-chip in which flow measurement is crucial, such as flow cytometry and particle separation applications.
A PDMS-based gas permeation pump for on-chip fluid handling in microfluidic devices
Journal of Micromechanics and Microengineering, 2006
We demonstrate a non-contact pumping mechanism for the manipulation of aqueous solutions within microfluidic devices. The method utilizes multi-layer soft lithography techniques to integrate a thin polydimethylsiloxane (PDMS) membrane that acts as a diffusion medium for regulated air pressure and a vacuum. Pressurized microchannels filter air through the PDMS membrane due to its high gas permeability causing a pressure difference in the liquid channel and generating flow. Likewise, a vacuum can be applied to pull air through the membrane allowing the filling of dead-end channels and the removal of bubbles. Flow rates vary according to applied pressure/vacuum, membrane thickness and diffusion area. A gas permeation pump is an inexpensive alternative to other micropumps. The pump is easily integrated with highly arrayed multi-channel/chamber applications for micro-total analysis systems, fluid metering and dispensing, and drug delivery. Flow rates of 200 nl min-1 have been achieved using this technique. Successful localized fluid turning at intersections, fluid metering and filling of dead-end chambers were also demonstrated.