H-Shaped Beam Capacitive Acceleration Sensor
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Solution Overview
Problem
Existing capacitive acceleration sensors face challenges in achieving symmetrical beam-mass structures, leading to cross sensitivity and poor shock resistance, with current manufacturing methods being complex and costly, and resulting in nonuniform beam thickness and residual stress.
Innovation Solution
A method for preparing a capacitive acceleration sensor with an 'H'-shaped beam using anisotropic etching and photolithography to form symmetrical 'H'-shaped elastic beams, anti-overloading bumps, and damping grooves on a silicon substrate, ensuring accurate and controllable beam thickness and bonding process simplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If concentrated boron-doped self-stop method is used to fabricate symmetrical beam-mass structure, then beam thickness can be controlled, but nonuniform doping concentration results in nonuniform beam thickness and residual stress influences device performance
Solution Approach 1:
The patent extracts the doping process from the beam fabrication sequence, performing boron doping on the silicon wafer before the beam-mass structure is formed. This separates the doping operation from the subsequent etching and processing steps, allowing uniform doping concentration throughout the structure without affecting beam thickness uniformity or introducing residual stress that would compromise device performance.
Solution Approach 2:
The patent applies preliminary boron doping to the silicon wafer substrate before forming the beam-mass structure through etching. This preliminary action ensures that the doping is uniformly distributed across the entire wafer surface, including future beam regions, thereby preventing nonuniform thickness and residual stress issues that would arise from post-fabrication doping attempts.
2Shape
If heterogeneous self-stop method with silicon oxide beam is used, then symmetrical beam-mass structure can be formed, but silicon oxide beam has poor shock resistance due to limited thickness
Solution Approach 1:
The patent changes the material parameter from silicon oxide to bulk silicon for the beam structure. By using bulk silicon instead of thin silicon oxide layers, the beam achieves both the required symmetry and significantly improved shock resistance. The bulk silicon material provides inherent mechanical strength while maintaining the symmetrical geometry necessary for reducing cross sensitivity.
3Shape
If double layer bonded silicon beam method is used, then symmetrical beam-mass structure is formed, but the process is very complicated and cost is comparatively high
Solution Approach 1:
The patent merges the beam and mass structure into a single integrated component formed by anisotropic etching of the silicon wafer. This consolidation eliminates the need for separate beam and mass fabrication steps, as well as subsequent bonding operations, thereby significantly simplifying the manufacturing process while maintaining the required symmetrical geometry.
Solution Approach 2:
The patent employs self-aligned anisotropic etching processes where the etching pattern automatically defines both the beam and mass structure boundaries. The process self-determines the symmetrical geometry without requiring complex alignment procedures or additional bonding steps, thereby reducing manufacturing complexity and cost.
4Ease of manufacture
If beam is simply placed on one surface of seismic mass with asymmetric configuration, then manufacturing is simplified, but transverse acceleration causes beam bending and increases cross sensitivity
Solution Approach 1:
The patent applies asymmetry in reverse by creating a symmetrical configuration where the beam-mass structure is formed with equal geometry on both sides of the seismic mass. This symmetrical design ensures that transverse accelerations produce equal and opposite effects on both sides, causing the beam to remain balanced and preventing bending that would increase cross sensitivity, while still maintaining manufacturing simplicity through unified process steps.
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 method results in a capacitive acceleration sensor with improved resistance to lateral and torsional impacts, reduced cross sensitivity, and enhanced manufacturing precision, simplifying the process while maintaining high symmetry and accuracy.
Implementation Method 1
performing etching at two surfaces of an oxygen containing silicon substrate having a double device layer based on an anisotropic etching method
Implementation Method 2
forming a plurality of anti-overloading bumps at recesses on the two surfaces based on photolithography and the anisotropic etching method
Implementation Method 3
simultaneously bonding the first electrode structural layer, the structure comprising the released 'H'-shaped elastic beams and the seismic mass, and the second electrode structural layer based on a bonding process
Data Source
AI summary
A capacitive acceleration sensor with an “H”-shaped beam and a preparation method. The sensor at least includes: a first electrode structural layer, a middle structural layer and a second electrode structural layer; the first electrode structural layer and the second electrode structural layer are provided with electrode lead via holes, respectively; the middle structural layer includes: a frame formed at SOI silicon substrate having a double device layer, a seismic mass whose double sides are symmetrical, and an “H”-shaped elastic beam whose double sides are symmetrical, with one end connected to the frame and the other end connected to the seismic mass, there are anti-overloading bumps and damping grooves symmetrically provided on the two sides of the seismic mass, and the “H”-shaped elastic beam and a bulk silicon layer of the oxygen containing silicon substrate satisfy the requirements therebetween:√{square root over (2)}(a+b+c)<h, √{square root over (2)}d<h.