Oxide Semiconductor UV Sensor Circuit Reducing Dark Current
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Solution Overview
Problem
Conventional ultraviolet light sensors using silicon photodiodes face limitations in temperature range, reliability, and manufacturing cost due to high dark current and sensitivity to visible light, which restricts their application in portable electronic devices.
Innovation Solution
Employing an oxide semiconductor with a higher band gap, such as IGZO-based, and controlling the gate potential of transistors to prevent threshold voltage shifts, thereby enhancing sensitivity and reliability while reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon photodiode is used for ultraviolet light detection, then the sensor can detect ultraviolet light, but the dark current increases significantly with temperature rise, narrowing the usable temperature range
Solution Approach 1:
The patent changes the fundamental material parameter (band gap) from silicon (1.1 eV) to oxide semiconductor (3.2 eV), which fundamentally alters the temperature dependence of dark current. This parameter change enables operation across a wide temperature range from -40°C to 85°C while maintaining low dark current levels.
Solution Approach 2:
The patent employs an IGZO-based oxide semiconductor composite material that combines indium oxide, gallium oxide, and zinc oxide in specific ratios. This composite structure provides both the wide band gap for low dark current and the appropriate absorption characteristics for ultraviolet detection.
2Measurement precision
If the sensitivity to ultraviolet light is increased by adjusting the silicon photodiode structure, then ultraviolet detection performance improves, but the manufacturing cost increases
Solution Approach 1:
The patent achieves high ultraviolet sensitivity through inherent material properties of oxide semiconductors rather than complex structural modifications. The wide band gap of 3.2 eV naturally provides high sensitivity to ultraviolet light while maintaining simplicity in device structure, thereby reducing manufacturing costs.
3Reliability
If continuous ultraviolet light irradiation is applied to a silicon photodiode, then the sensor can measure ultraviolet doses, but the photodiode degrades and reliability decreases
Solution Approach 1:
The patent uses an IGZO-based oxide semiconductor composite that exhibits superior resistance to ultraviolet-induced degradation compared to silicon. The specific composition ratio of In:Ga:Zn = 1:1:1 provides enhanced stability and longevity under continuous ultraviolet irradiation, extending the service life of the sensor.
4Measurement precision
If a filter is added to selectively transmit ultraviolet light, then sensitivity to ultraviolet light increases, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent achieves spectral selectivity through the fundamental optical parameter of the oxide semiconductor material itself. The wide band gap of 3.2 eV inherently provides high absorption for ultraviolet light while being transparent to visible light, eliminating the need for additional filter structures and simplifying the overall device design.
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 a sensor circuit with increased sensitivity to ultraviolet light, improved reliability, and a wider temperature range of operation, expanding its application in portable electronic devices.
Implementation Method 1
an oxide semiconductor having a higher band gap than silicon, specifically, an IGZO-based oxide semiconductor that contains In, Ga, and Zn, is used for detecting ultraviolet light
Implementation Method 2
a transistor including a channel formation region in an oxide semiconductor is used, and the amount of off-state current flowing through the transistor during ultraviolet light irradiation is measured
Data Source
AI summary
A sensor circuit includes a transistor comprising an oxide semiconductor; a first circuit which supplies one of a first potential and a second potential; a first switch; a second switch; and a second circuit to which a current flowing between a source and a drain of the transistor is applied via the second switch when the first potential is applied to a gate of the transistor. The first potential is lower than a potential of the source or a potential of the drain of the transistor, and the second potential is higher than the potential of the source or the potential of the drain of the transistor. The first switch electrically connects the source and the drain of the transistor when the second potential is applied to the gate of the transistor, and electrically isolates them when the first potential is applied to the gate of the transistor.