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

Abstract

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.

Stiction of parylene C to silicon surface measured using blister tests

“…After performing blister tests, stiction was quantified. The results are consistent with other studies performed on thin polymeric films such as polyimide [3]. Experiments show that mechanisms that can reduce the proximity between parylene and silicon surfaces during drying will likely reduce stiction since stiction results from the hydrophobic interaction between silicon and parylene surfaces due to proximity.…”

“…Attempts have been made to reduce stiction. For example, a surface treated valve with Cr/Au coating and O 2 plasma showed cracking pressure of 20-40kPa [8]; the cracking pressure of a polyimide check valve with C 4 F 8 /Ar non-stiction coating changed from 210kPa to 59kPa [3]; and SAM (self-assembled monolayer) is also used to reduce stiction [7]. For parylene check valves, since stiction governs the cracking pressure of the valves, it must be controlled instead of blindly reduced.…”

PDMS Selective Bonding for the Fabrication of Biocompatible All Polymer NC Microvalves

“…This technique has led to a lower release pressure compared to similar techniques in literature (e.g. non stiction coatings [24]). The fabrication and performance of the microvalve are described in detail in the next sections.…”

Lab-on-a-Chip and Fluid Manipulation Applications

“…In an effort to develop a micro-gas chromatography system (see discussion below), Bae et al developed a bi-directional electrostatic microvalve that can switch a gas flow in less than 100 µs under high-pressure operation [24]. Another key component is a hydrophobic layer deposited on every touching interface to prevent any stiction from occurring and to reduce the required valve opening pressure [25,26]. When a voltage is applied between the valve opening electrode and membrane electrode (while removing it between the other two), the movable membrane is deflected toward the valve seat, opening the flow path from A to C. High-pressure operation can be achieved as the pneumatic pressure is applied to the other side of the membrane electrode to either enhance the hold up pressure or increase the closing speed.…”