Transduction Mechanism
Microelectromechanical pressure sensing structures convert physical deflection into electrical capacitance variations across a micro-machined gap. A capacitive mems pressure sensor utilizes a flexible silicon diaphragm suspended over a fixed cavity to form a variable capacitor. Applied pressure deforms the diaphragm, narrowing the gap and increasing output capacitance according to electro-static equations.
Measurement range is limited by mechanical stop contact or structural yield under overpressure conditions. High sensitivity models operate near the pull-in voltage threshold where electrostatic forces threaten to collapse the membrane onto the substrate.
Diaphragm Mechanics
Flexural stiffness governed by silicon membrane thickness determines displacement per unit pressure. Uniform etching yields predictable mechanical response across micro-machined sensor dies. Built-in residual stresses from thin film deposition shift nominal diaphragm zero positions.
Overpressure stops prevent membrane fracture during severe pressure spikes in field applications.
Signal Conditioning
Capacitance changes on the order of femtofarads require high frequency excitation circuits to generate readable voltage signals. Switched capacitor integrated circuits convert low capacitance variations into analog or digital outputs. Stray capacitance from packaging leads introduces baseline offsets that must be subtracted during factory calibration.
On-chip compensation networks mitigate gain shifts caused by ambient temperature changes.
Environmental Influence
Humidity ingress changes the dielectric constant of air inside open cavity reference structures. Temperature variations induce differential thermal expansion between the silicon die and package substrate, producing spurious stress signals. Hermetic sealing protects internal cavity references from moisture ingress and atmospheric contamination.
Metrological verification requires pressure cycling across full thermal ranges to establish long-term drift characteristics.
