Capacitive Acceleration Sensor with Monolithic CMOS Integration
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Solution Overview
Problem
Conventional methods for manufacturing capacitive acceleration and gyro sensors on semiconductor substrates are complex and limit miniaturization due to the need for high-temperature epitaxial growth and multiple layer processing, which restricts integration with CMOS devices and increases package size and cost.
Innovation Solution
A semiconductor device with a capacitive acceleration sensor and CMIS transistor integrated on the same substrate, featuring interdigital electrodes and a simplified manufacturing process that avoids high-temperature epitaxial growth, allowing for reduced package size and improved detection accuracy by forming electrodes directly on the substrate surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth and multiple layer processing are used to manufacture capacitive sensors, then the sensors can be fabricated with proper electrode structures, but the manufacturing process becomes complex and package size increases
Solution Approach 1:
The patent extracts and eliminates the complex epitaxial growth process and sacrificial layer methodology from the manufacturing flow. Instead of forming electrodes through multiple deposition and etching steps, the invention directly utilizes the semiconductor substrate itself to form the electrode structures, taking out the unnecessary intermediate processing steps while maintaining the functional electrode structure.
Solution Approach 2:
The patent merges the substrate function with the electrode function. The semiconductor substrate serves dual purposes: as the mechanical support structure and as the electrode material itself. This combining of functions eliminates the need for separate electrode formation processes, reducing manufacturing complexity while achieving the same capacitive sensor functionality.
2Manufacturing precision
If high-temperature epitaxial growth is used to form electrodes, then proper electrode material properties are achieved, but integration with CMOS devices is restricted due to temperature constraints
Solution Approach 1:
The patent replaces the thermal/chemical process of epitaxial growth with a direct mechanical/utilization approach. Instead of using high-temperature chemical vapor deposition to grow polysilicon electrodes, the invention directly utilizes the existing semiconductor substrate material as the electrode, eliminating the need for high-temperature processing and enabling compatibility with temperature-sensitive CMOS devices.
3Reliability
If multiple sacrificial layers and epitaxial growth steps are employed, then movable electrodes can be formed floating above fixed electrodes, but the number of processing steps increases and productivity decreases
Solution Approach 1:
The patent extracts and removes the sacrificial layer formation and removal steps from the manufacturing process. Instead of depositing sacrificial layers, forming openings, growing epitaxial structures, and then removing sacrificial material, the invention directly forms the movable electrodes using the substrate itself, taking out the unnecessary intermediate steps while maintaining the floating electrode structure reliability.
Solution Approach 2:
The patent performs preliminary structuring of the substrate before sensor fabrication. The substrate is pre-patterned and prepared with the necessary electrode geometries and cavity structures before the actual sensor assembly process, eliminating the need for subsequent complex multi-step electrode formation processes and improving manufacturing throughput.
4Manufacturing precision
If conventional sensor manufacturing is used separate from integrated circuits, then each component can be optimized independently, but package size increases and wire bonding is required
Solution Approach 1:
The patent merges the sensor fabrication process with the CMOS integrated circuit fabrication process into a single unified manufacturing flow. Both the capacitive sensor electrodes and the CMOS circuit elements are formed on the same semiconductor substrate using compatible processing steps, enabling monolithic integration that reduces package size and eliminates the need for separate wire bonding operations.
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
The solution enables precise acceleration detection across three axes with reduced package size and cost, simplified wiring, and enhanced detection accuracy by eliminating the need for bonding wires and reducing manufacturing complexity.
Implementation Method 1
detecting change in capacitance between electrodes (between a fixed electrode and a movable electrode) opposed to each other
Implementation Method 2
The gyro sensor detects angular velocities acting around the respective axes through Coriolis force acting on the respective vibrators when the sensor inclines
Data Source
AI summary
A semiconductor substrate of a semiconductor device has a sensor region and an integrated circuit region, and a cavity is formed immediately under a surface layer portion of the sensor region. A capacitive acceleration sensor is formed on the sensor region by working a surface layer portion of the semiconductor substrate opposed to the cavity. The capacitive acceleration sensor includes an interdigital fixed electrode and an interdigital movable electrode. A CMIS transistor is formed on the integrated circuit region. The CMIS transistor includes a P-type well region and an N-type well region formed on the surface layer portion of the semiconductor substrate. A gate electrode is opposed to the respective ones of the P-type well region and the N-type well region through a gate insulating film formed on a surface of the semiconductor substrate.