Photodiode Shield Layer Layout for Stable Optical Detection Signals
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Solution Overview
Problem
Optical sensors used for detecting fingerprint and vein patterns face errors due to parasitic diodes and parasitic capacitance, which affect the accuracy of detection signals.
Innovation Solution
A detection device is designed with a photodiode configuration that includes a substrate, a lower electrode, a lower buffer layer, an active layer, an upper buffer layer, and an upper electrode, along with a signal line and a shield layer. The shield layer is supplied with a reference voltage to reduce parasitic capacitance and capacitive coupling between the photodiode and the signal line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode structure with upper and lower electrodes and buffer layers is used, then the photodiode can effectively detect optical signals, but parasitic diodes and parasitic capacitance are generated between signal lines and the upper electrode, causing coupling and potential variation
Solution Approach 1:
A shield layer is introduced as an intermediary component between the signal line and the photodiode's upper electrode. This shield layer, connected to ground potential, acts as a mediator that blocks the capacitive coupling path and prevents parasitic effects from affecting the signal line, thereby eliminating the harmful interaction while maintaining the photodiode's detection functionality
Solution Approach 2:
The patent converts the harmful parasitic capacitance effect into a beneficial shielding effect by strategically placing a conductive shield layer at ground potential. The same capacitive coupling mechanism that causes harm is redirected to couple the signal line to ground through the shield, transforming the parasitic effect into a protective shielding effect that stabilizes the signal line potential
2Ease of operation
If signal lines are placed close to the photodiode for electrical coupling, then the detection circuit can receive signals, but leakage from parasitic diodes varies the potential of signal lines, causing errors in detection signals
Solution Approach 1:
The shield layer serves as a protective intermediary positioned between the signal line and the photodiode structure. It provides a controlled capacitive coupling path to ground, preventing uncontrolled leakage currents from parasitic diodes from affecting the signal line potential, thereby maintaining both electrical coupling efficiency and potential stability
Solution Approach 2:
The shield layer is maintained at ground potential (equipotential reference), which stabilizes the electrical environment around the signal line. By providing a defined potential reference, it prevents potential variations caused by parasitic diode leakage, ensuring reliable signal transmission while maintaining ease of electrical coupling
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 configuration improves the accuracy of detection signals by reducing parasitic capacitance and unintended capacitive coupling, leading to enhanced detection performance.
Implementation Method 1
If parasitic diodes and parasitic capacitance are generated between a plurality of signal lines and the upper electrode of the photodiodes, coupling occurs between the parasitic diodes and the signal lines via the parasitic capacitance
Data Source
AI summary
According to an aspect, a detection device includes: a substrate; a photodiode that is provided on the substrate and in which a lower electrode, a lower buffer layer, an active layer, an upper buffer layer, and an upper electrode are stacked on the substrate in the order as listed; a signal line that is provided between the substrate and the photodiode in a direction orthogonal to the substrate and is electrically coupled to the lower electrode of the photodiode; a detection circuit electrically coupled to the photodiode via the signal line; and a shield layer that is provided between the signal line and the lower buffer layer in the direction orthogonal to the substrate and is configured to be supplied with a reference voltage.