MEMS SOI Pressure Sensor Annealing and Trench Design
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Solution Overview
Problem
Existing MEMS SOI piezoresistive pressure sensors face instability due to surface damage from over-etching and trapped charges, and low sensitivity, primarily caused by defects in the buried oxide layer and interface issues during varistor doping.
Innovation Solution
A MEMS SOI pressure sensor design featuring a bulk silicon layer with a cavity, a buried oxide layer, and varistors connected in a Wheatstone bridge, where the surface damage from over-etching is repaired using annealing in an oxygen atmosphere to form a high-quality SiO2 passivation layer, and a trench is formed below the varistor to prevent impurity defects, enhancing stability and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If over-etching is performed to ensure complete etching of the device layer, then the varistor isolation is improved, but surface damage to the buried oxide layer occurs causing defects and charge trapping
Solution Approach 1:
The patent applies preliminary action by performing annealing treatment on the buried oxide layer before the etching process. This pre-treatment strengthens the oxide layer surface, making it more resistant to damage from subsequent over-etching operations. The annealing process creates a more robust surface structure that can withstand the etching conditions while still allowing complete device layer removal and proper varistor isolation.
Solution Approach 2:
The patent implements beforehand cushioning by introducing a protective layer or treatment on the buried oxide layer prior to etching. This protective measure acts as a cushion against the harmful effects of over-etching, preventing surface damage and charge trapping while still allowing the etching process to achieve complete device layer removal and proper varistor isolation.
2Measurement precision
If sensitivity is increased to improve device performance, then detection capability is improved, but design difficulty of interface circuit increases
Solution Approach 1:
The patent applies parameter changes by optimizing the electrical parameters of the varistor (such as resistance value, doping concentration, or geometric dimensions) to achieve the desired sensitivity level. By carefully adjusting these parameters, the sensor achieves high detection capability while keeping the output signal within a range that simplifies interface circuit design and signal conditioning requirements.
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 effectively improves sensor stability by repairing surface damage and reducing defects, while the trench structure increases sensitivity through stress concentration, resulting in a more reliable and sensitive pressure sensor.
Implementation Method 1
the damage to a surface of the buried oxide layer as a result of over-etching during formation of the varistor by means of photolithography is repaired by means of the annealing treatment
Implementation Method 2
The varistor is obtained by means of photolithography and ion implantation on a device layer of an SOI wafer
Implementation Method 3
The MEMS piezoresistive pressure sensor is a device formed by means of the piezoresistive effect of single crystal silicon
Data Source
AI summary
The present invention discloses a micro-electro-mechanical system silicon on insulator (MEMS SOI) pressure sensor and a method for preparing the same. The pressure sensor includes a bulk silicon layer, a buried oxide layer, a substrate, a varistor, a passivation layer, and an electrode layer. The varistor is obtained by means of photolithography and ion implantation on a device layer of an SOI wafer. The passivation layer is SiO2 formed by means of annealing treatment on the SOI wafer. An annealing atmosphere is one of pure O2, a gas mixture of O2/H2O, a gas mixture of O2/NO, a gas mixture of O2/HCl, and a gas mixture of O2/CHF3. By means of the annealing treatment, the damage to a surface of the buried oxide layer as a result of over-etching during formation of the varistor by means of photolithography is eliminated and the unstability of the sensor caused by body and interface defects of the passivation layer and trapped charges thereof is resolved. A trench is formed at the buried oxide layer and the bulk silicon layer directly below the varistor, which helps overcome defects as a result of doped impurities entering the buried oxide layer below the varistor, and helps improve the sensitivity of the sensor.