A normally closed in-channel micro check valve

144

101

Parylene C, an emerging material in microelectromechanical systems, is of particular interest in biomedical and lab-on-a-chip applications where stable, chemically inert surfaces are desired. Practical implementation of Parylene C as a structural material requires the development of micropatterning techniques for its selective removal. Dry etching methods are currently the most suitable for batch processing of Parylene structures. A performance comparison of three different modes of Parylene C plasma etching was conducted using oxygen as the primary reactive species. Plasma, reactive ion and deep reactive ion etching techniques were explored. In addition, a new switched chemistry process with alternating cycles of fluoropolymer deposition and oxygen plasma etching was examined to produce structures with vertical sidewalls. Vertical etch rates, lateral etch rates, anisotropy and sidewall angles were characterized for each of the methods. This detailed characterization was enabled by the application of replica casting to obtain cross sections of etched structures in a non-destructive manner. Application of the developed etch recipes to the fabrication of complex Parylene C microstructures is also discussed.

Section: Introductionmentioning

confidence: 99%

Plasma removal of Parylene C

Meng¹,

Li²,

Tai³

2008

144

101

“…A number of different methods have been developed to reduce stiction including soaking with low surface energy solvents before drying, using self-assembled monolayer (SAM) coatings [1], plasma deposition of hydrophobic polymer coatings [9][10][11][12] and oxygen plasma treatments [2,12]. A hydrophobic fluorocarbon (CF n ) film coating has been investigated [4,[13][14][15][16] that is formed by exposing a surface to a C 4 F 8 /Ar discharge in an inductively coupled plasma (ICP).…”

Section: Introductionmentioning

confidence: 99%

Surface energy approach and AFM verification of the (CF)_ntreated surface effect and its correlation with adhesion reduction in microvalves

Han

Yeom

Mensing

et al. 2009

The purpose of this paper is to outline an approach that will determine the optimal surface pairs to use in a MEMS device with demonstrated stiction problems. The approach uses the contact angle and atomic force microscopy (AFM) pull-off measurements to predict adhesion at the solid-solid interface. The results are compared to microvalves that have been fabricated with different surfaces at the seat/membrane interface. For microfabricated mechanical devices with surfaces that touch or have a small gap distance, stiction can occur during fabrication or during use. Fabricating multiple devices with different surfaces to determine the lowest stiction can be costly and time consuming. Identifying the surface pair with the least amount of surface adhesion before fabrication can lead to a reduction in device failure due to stiction, and/or time it takes to find the lowest energy surfaces via trial and error. Surface energies are obtained using the van Oss equation based on the contact angle measurements, and surface energy can be used to show the relative adhesions between two surface pairs. An AFM pull-off test is performed using nano-and micro-sized tips to quantify the effect of the different surfaces on adhesion between the solid-solid surface pairs, including SiO 2 /PI, CF n /PI, CF n /SiO 2 and CF n /CF n . The work of adhesion of the surface pairs is obtained using the Derjaguin-Muller-Toporotov (DMT) and Johnson-Kendall-Roberts (JKR) theories. The surfaces treated with a C 4 F 8 /Ar plasma to form a CF n coating showed the least amount of surface adhesion. The CF n surface treatment effects on adhesion are quantified and correlated with the reduction in the opening pressure of the microvalve whose interfaces are coated with a CF n film. The AFM pull-off test was more closely related to adhesive forces between the surfaces of the valves as seen in the opening pressure data. The adhesion calculation based on the contact angle measurements predicts the adhesion force with a similar trend but does not take into account the meniscus forces.

“…Many passive check valves consist of a cantilever or membrane on a valve-seat surface [1,2,9,10,[12][13][14], and tight sealing between the two surfaces induces bonding forces.…”

Section: Introductionmentioning

confidence: 99%

Micro-fabricated membrane gas valves with a non-stiction coating deposited by C₄F₈/Ar plasma

Han

Flachsbart

Masel

et al. 2008

Micro-fabricated gas valves with C4F8/Ar treatment at the sealing interface are designed, fabricated and characterized to passively control gases in a micro gas analysis system. The check valves form a seal between a polished Si/SiO2 substrate and a smooth polyimide (PI) membrane. The smooth PI membrane touches the SiO2 surface, giving rise to relatively strong van der Waals adhesion, and under humid conditions hydrogen-bonded stiction can occur at the interface between PI and SiO2. To prevent stiction from dominating adhesion, the valve-seat surface was treated with a hydrophobic CFn thin film, which was formed by exposing the surface to C4F8/Ar inductively coupled plasma (ICP) at low power. The valves without a non-stiction coating did not open with inlet pressures up to 210 kPa. With a non-stiction coating, the valves showed an average initial opening pressure of 59.25 kPa. In order to further reduce the opening pressure, 40% of the valve-seat area is reduced. After modification, the average opening pressure is reduced to 32.5 kPa. After the initial opening, the average in-use opening pressure was 16.9 kPa before area modification, and 13.1 kPa after the modification. The valve has been tested up to 10 000 open/close cycles under dry N2 gas flow, and an additional 3000 open/close cycles under humid N2 gas flow. The average forward flow conductance of the valves before modification was 1.1 sccm kPa−1, and the conductance after modification was 1.41 sccm kPa−1. The measured leakage is between 0.0003 and 0.004 sccm up to 35 kPa reverse pressure.