MEMS Glass Charging Control via Midpoint Voltage
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Solution Overview
Problem
In Micro-Electro-Mechanical Systems (MEMS) devices, exposed glass layers can accumulate electrical charges, affecting the sensitivity and reliability of sensors like gyroscopes and accelerometers, leading to unstable performance metrics.
Innovation Solution
Applying a first voltage to the sense plate and a second voltage to the outboard metallization layer, with a predetermined voltage level difference, ensures the exposed glass portion has an average voltage midway between the two, thus neutralizing its impact on sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uncovered glass is exposed to the proof mass in a capacitive MEMS sensor, then the device structure is simplified and glass conductivity is utilized, but the effective sensitivity changes as charge accumulates on the glass during operation
Solution Approach 1:
The patent applies equipotentiality by connecting the exposed glass portion to the same electrical potential as the proof mass through a conductive path. This ensures that no voltage difference exists between the glass and proof mass, preventing charge accumulation on the glass surface. By maintaining equal potentials, the harmful capacitive effect is eliminated while preserving the simplified structural design.
2Reliability
If glass layers are doped to provide conductivity, then electrical charges can flow and accumulate on the glass, but this makes the scale factor and bias unreliable
Solution Approach 1:
The patent extracts the harmful capacitive effect by removing the voltage difference between the glass and proof mass. By establishing a direct conductive connection that equalizes potentials, the charge accumulation mechanism is eliminated. The doped glass retains its conductivity for structural purposes but no longer generates harmful capacitive effects because there is no potential difference to drive charge accumulation.
3Duration of action of moving object
If exposed glass accumulates charge during operation, then the glass potential varies over time, but this degrades sensor performance metrics
Solution Approach 1:
The patent applies preliminary action by establishing the conductive connection and equalizing potentials before charge accumulation can occur during operation. The conductive path is built into the device structure during manufacturing, ensuring that the glass and proof mass remain at the same potential throughout the device's operational life. This preventive measure eliminates time-varying glass charging effects from the outset.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively controls glass charging, ensuring it does not degrade sensor performance over time by maintaining the glass potential equal to that of the proof mass, thereby eliminating the effects of time-varying glass charging on sensor capacitance.
Implementation Method 1
These glass layers are typically doped, which results in the glass having some conductivity, allowing electrical charges to flow and accumulate on the glass during operation
Implementation Method 2
applying a first voltage to the sense plate and a second voltage to the outboard metallization layer. The first voltage is separated from the second voltage by a predetermined voltage level such that the exposed glass portion has an average voltage corresponding to a voltage midway between the first voltage and the second voltage
Data Source
AI summary
A method of controlling exposed glass charging in a micro-electro-mechanical systems (MEMS) device is disclosed. The method includes providing a MEMS device comprising a proof mass positioned apart from at least one sense plate and at least one outboard metallization layer, wherein at least one conductive glass layer is coupled to the sense plate and the outboard metallization layer, the conductive glass layer including at least one exposed glass portion near the proof mass; and applying a first voltage to the sense plate and a second voltage to the outboard metallization layer. The first voltage is separated from the second voltage by a predetermined voltage level such that the exposed glass portion has an average voltage corresponding to a voltage midway between the first voltage and the second voltage.