MEMS Microphone Substrate Impurity for Photoelectric Noise Reduction
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Solution Overview
Problem
Conventional MEMS microphones suffer from noise generation due to the photoelectric effect when light strikes the semiconductor substrate, affecting accurate sound pressure signal output.
Innovation Solution
A MEMS acoustic transducer with a semiconductor substrate, a conductive vibrating membrane, and a fixed electrode plate, where an impurity is added to the surface of the semiconductor substrate to reduce the lifetime of electrons and holes generated by light, thereby minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a semiconductor substrate is used in the MEMS microphone, then miniaturization and digitalization compatibility are improved, but noise is generated when light strikes the substrate due to the photoelectric effect
Solution Approach 1:
The patent converts the harmful photoelectric effect into a beneficial outcome by intentionally adding impurities to the semiconductor substrate. These impurities shorten the carrier lifetime, causing electrons and holes to recombine quickly before they can generate noise currents, thus transforming the potential harm of light exposure into a neutral or beneficial effect
Solution Approach 2:
The patent changes the physical-chemical parameters of the semiconductor substrate by adding specific impurities (such as gold, iron, or nickel at controlled concentrations). This parameter change fundamentally alters the carrier lifetime from a long duration (causing noise) to a short duration (reducing noise), thereby solving the contradiction between using semiconductor substrates and avoiding light-induced noise
2Power
If the semiconductor substrate has no impurity added, then the electrical signal output is strong, but light-induced noise is generated due to long electron-hole lifetime
Solution Approach 1:
The patent applies local quality by adding impurities specifically to certain regions of the semiconductor substrate where light exposure occurs. This creates a non-uniform impurity distribution that locally reduces carrier lifetime in noise-prone areas while maintaining overall substrate functionality and signal strength
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 addition of an impurity to the semiconductor substrate reduces the electric current caused by light, leading to lower noise levels and improved accuracy in detecting sound pressure.
Implementation Method 1
when light strikes the semiconductor substrate constituting the microphone, then due to a photoelectric effect, there occurs a phenomenon in which electrons and holes are generated from atoms and recombined with each other. Then, an electric current is generated in the process of generation and combination of electrons and holes.
Implementation Method 2
The acoustic sensor includes a diaphragm electrode and a back plate electrode that are provided on a semiconductor substrate so as to form a capacitor. When a sound pressure is applied to this MEMS sensor, a conductive vibrating membrane (diaphragm) vibrates, and the distance between the vibrating membrane and a fixed membrane (back plate) including a fixed electrode changes. This leads to change in capacitance of the capacitor formed by the vibrating membrane and the fixed electrode.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(c)
AI summary
In an acoustic sensor (1) of the present invention, a conductive vibrating membrane (14) and a fixed electrode plate (5) are disposed above a silicon substrate (11) with an air gap (22) provided therebetween, and the substrate (11) has an impurity added to a surface thereof.