MEMS Hermetic Seal Testing via Vacuum Prober Q Factor
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Solution Overview
Problem
Existing methods for hermeticity testing of MEMS devices, particularly those with CMOS ASIC caps, struggle to reliably distinguish leaky devices from hermetically sealed ones at ambient pressures, as the sensitivity of Q factor measurements is compromised by internal pressures above 1 atmosphere.
Innovation Solution
Conducting resonant frequency testing in a vacuum prober with reduced ambient pressure below 200 mbar or by varying temperature to differentiate Q factor changes, allowing for the identification of leaking devices based on their distinct Q factor responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If resonant frequency testing is conducted at ambient pressure, then testing can be performed easily, but Q factor measurements cannot reliably distinguish leaky devices from hermetically sealed devices when internal pressures are above 1 atmosphere
Solution Approach 1:
The patent changes the ambient pressure parameter from atmospheric pressure to vacuum pressure (below 200 mbar). This parameter change enables Q factor measurements to reliably distinguish between leaky and hermetically sealed devices even when internal chamber pressures are above 1 atmosphere, resolving the measurement sensitivity problem while maintaining testing feasibility through automated vacuum prober systems
2Reliability
If vacuum bonding is used to create hermetic seals, then device hermeticity is improved, but Q factor measurements at atmospheric pressure cannot detect leaking devices
Solution Approach 1:
The patent uses vacuum as an inert environment for testing. By conducting resonant frequency measurements in a vacuum chamber (below 200 mbar), the testing environment becomes insensitive to internal chamber pressure variations, allowing reliable detection of hermetic seal integrity through Q factor measurements regardless of whether devices were vacuum-bonded or capped at elevated pressures
Solution Approach 2:
The testing ambient pressure parameter is changed from atmospheric to vacuum conditions. This enables the detection system to distinguish between leaky and sealed devices based on Q factor differences that are only visible under vacuum conditions, solving the leak detection problem for vacuum-bonded devices
3Reliability
If devices are capped to maintain pressures significantly away from one atmosphere, then device functionality is maintained, but resonant frequency testing at atmospheric pressure cannot detect leaking devices
Solution Approach 1:
The patent changes the testing ambient pressure to vacuum (below 200 mbar), which creates a pressure differential that makes Q factor measurements sensitive to leaks regardless of the internal chamber pressure. This allows devices capped at various pressures (including above atmospheric pressure) to be reliably tested for hermeticity without compromising their functional operating conditions
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
Effectively separates leaking MEMS devices from sealed ones, even when internal pressures are above 500 mbar, ensuring reliable manufacturing and packaging of high-quality MEMS devices.
Implementation Method 1
Ambient pressure within the vacuum prober is reduced to a pressure below that in the chamber of a MEMS device on the wafer. In a preferred embodiment, the pressure is reduced below 200 mbar.
Implementation Method 2
Resonant frequency testing determines for each device a measure of the resonant frequency and a measure of quality factor (Q).
Implementation Method 3
Resonant frequency testing is conducted at a first temperature. The wafer is then brought to a second temperature on the wafer prober. Resonant frequency testing is conducted at the second temperature on the wafer prober.
Data Source
AI summary
Manufactured capped MEMS device wafers are tested for hermeticity on a vacuum prober at differing pressures or on a wafer prober at differing temperatures. Resonant frequency testing is conducted. Leaking MEMS devices are distinguished from the remaining MEMS devices on the basis of quality factor (“Q”) measurements obtained from the resonant frequency testing.