1 Mems Lubricating Air Bubble Array

Single atomic monolayer (SAM) technology will be used to design an air bubble array for the lubrication of MEMS devices with sliding and rotating parts. Patterning a matrix of hydrophobic patches on a hydrophilic substrate will result in an array of air bubbles formed by the repulsive behavior of water molecules with the hydrophobic surfaces. The performance of the air bubble array will be determined by using a serpentine spring force gauge to measure the static friction required to pull a hydrophilic shuttle across the patterned substrate. Force calculations for air bubbles under hydrostatic pressure and a uniaxial compressive load show that the air bubbles will be able to withstand the external forces acting upon it. INTRODUCTON In MEMS devices with sliding and rotating parts, friction forces are the limiting factor to the successful performance of the device [1]. Previous work investigating the friction forces in micromotors suggests that hydrophobic lubricants are ideal for MEMS lubrication [1]. Alongside friction, adhesion is a common problem, especially in the fabrication process of various MEMS devices. Subjecting a structure to an aqueous rinse and dry cycle can form strong capillary forces that cause the collapse of beams and plates [1]. The application of a self-assembled monolayer (SAM) is a popular technique for creating hydrophobic surfaces that repel water to prevent adhesion [1,3-5]. There have also been recent studies on using SAM technology for fluid directing and fluidic self-assembly by patterning hydrophobic-hydrophilic surfaces [6,7]. This report investigates the use of SAM technology to design an air bubble array for the lubrication of MEMS devices with sliding and rotating parts. Patterning a matrix of hydrophobic patches on a hydrophilic substrate will result in an array of air bubbles formed by the repulsive behavior of water molecules with the hydrophobic surfaces (see Figure 1). If a hydrophilic mate piece is placed on top of the patterned substrate, the air bubbles will provide a buffer between the surfaces as long as the bubbles remain intact. Force calculations for a bubble under hydrostatic pressure and a uniaxial compressive load are in the Expected Results section. Figure 1: Schematic of hydrophobic-hydrophilic patterned substrate with resulting air bubble formation. The performance of the air bubble array will be determined by using a serpentine spring force gauge to measure the