Multi-Channel MEMS Acoustic Isolator Without High-Bias Wire Bonding
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Solution Overview
Problem
Existing digital isolators face challenges with high DC bias voltage requirements and wire-bonding needs in back-to-back bonded structures, which can be risky for sensitive systems and limit them to single-channel operation.
Innovation Solution
A digital isolator device using piezoelectric resonators with through silicon openings and trenches to guide acoustic waves between stacked MEMS-based transmitter and receiver elements, eliminating the need for wire-bonding and enabling multi-channel operation without high DC bias voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back-to-back bonded structure is used, then galvanic isolation is achieved, but wire-bonding is required on both sides increasing complexity
Solution Approach 1:
The device is divided into two separate dice (first die with transmitter, second die with receiver) that are bonded back-to-back. Each die is independently wire-bonded to its carrier, eliminating the need for wire-bonding across the isolation barrier. This segmentation allows galvanic isolation to be achieved while reducing overall wiring complexity.
Solution Approach 2:
The piezoelectric crystal serves as an intermediary element between the two voltage domains. It converts electrical signals to mechanical vibrations on one side and converts mechanical vibrations back to electrical signals on the other side, enabling signal transmission without direct electrical connection and eliminating wire-bonding requirements across the isolation barrier.
2Productivity
If CMUT arrays are used to increase energy transfer, then transmission efficiency improves, but high DC bias voltage (120 V) is required creating safety risks
Solution Approach 1:
The invention changes the actuation mechanism from high-voltage capacitive actuation (CMUT) to low-voltage piezoelectric actuation (PMUT). This parameter change in the transduction mechanism eliminates the requirement for high DC bias voltage while maintaining effective mechanical vibration generation for acoustic wave transmission.
Solution Approach 2:
The invention replaces the capacitive micromachined ultrasonic transducer (CMUT) mechanism with a piezoelectric micromachined ultrasonic transducer (PMUT) mechanism. This substitution changes the physical principle from capacitive deformation under high voltage to piezoelectric deformation under low voltage, eliminating safety risks while maintaining ultrasound generation capability.
3Device complexity
If single-channel isolator is implemented, then device simplicity is maintained, but multi-channel operation is limited
Solution Approach 1:
The isolator device is designed with multiple independent transmitter-receiver channel pairs that can operate simultaneously. Each channel pair functions independently, allowing the device to handle multiple signal paths concurrently. This multi-functionality enables the isolator to serve various signal transmission needs within a single device package.
Solution Approach 2:
The invention transitions from single-channel to multi-channel operation by adding spatial dimensionality to the device structure. Multiple transmitter and receiver elements are arranged in arrays on respective dice, enabling parallel signal transmission across multiple channels while maintaining the compact back-to-back bonded architecture.
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 solution provides reliable and efficient digital isolation with multiple channels, reducing the risk of voltage-related issues and enabling compact, high-density digital isolator designs suitable for diverse applications.
Implementation Method 1
an upper die comprising a piezoelectric resonator for generating an acoustic signal
Implementation Method 2
a lower die comprising another piezoelectric resonator for receiving the acoustic signal
Implementation Method 3
the acoustic signal propagates through an opening formed through a substrate of the upper die below the piezoelectric resonator
Data Source
AI summary
Digital isolators in heterogenous system-in-package solutions are important devices for overcoming the challenge of managing the multiple voltage domains with different ground references. However, electronic digital isolators may be limited in their temperature range or be susceptible to electrostatic/electromagnetic fields which inherently result in electromagnetic interference. Micro-electromechanical systems (MEMS) based resonators are not susceptible to electromagnetic interference and through different materials can provide increased temperature operation. Accordingly, digital isolators exploiting vertical, lateral or side-by-side MEMS resonators to generate and receive acoustic waves, such as bulk acoustic waves, are outlined to provide such digital isolators.