Variable Sampling Verification Protocols for High Rate MEMS Gyroscope Lots
Variable sampling verification for high-rate MEMS gyroscopes optimizes lot acceptance by deriving continuous quality indices from dynamic rate table test samples.
Stiction Mitigation
Mitigation Strategy
Strategy or mechanism used to prevent the static friction between micro-scale components from causing them to adhere permanently. MEMS devices such as accelerometers and micromirrors require stiction mitigation to ensure that the moving parts do not get stuck during the manufacturing process or during use. It addresses the surface forces that dominate over gravity and inertia at the micron scale.
Surface Treatment
Applying hydrophobic coatings to the silicon surfaces reduces the capillary forces that pull the parts together when moisture is present. This form of stiction mitigation involves the deposition of self assembled monolayers that provide a low energy interface. These films must be thin enough to not interfere with the mechanical or electrical properties of the device.
Structural Design
Incorporating small bumps or dimples on the contact surfaces reduces the total area available for adhesion to occur. This physical approach to stiction mitigation limits the influence of Van der Waals forces and electrostatic attraction. Mechanical springs are also designed with sufficient restoring force to overcome any temporary sticking that might happen during a shock event.
Testing involves cycling the device through its full range of motion while monitoring the pull in and release voltages.
Process Environment
Drying the wafers using supercritical CO2 prevents the collapse of fine structures caused by the surface tension of evaporating liquids. This critical step in stiction mitigation ensures high yields during the final release of the microstructures. Clean and dry packaging is necessary to maintain these benefits throughout the life of the product.