Image Sensor Unit Pixel With Tunnel Junction Sensitivity Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors face limitations in high-density and high-speed frame image sensing due to small photo diode electrostatic capacity and sensitivity, requiring repetitive manufacturing processes to achieve optimal threshold voltage conditions.
Innovation Solution
A unit pixel with a tunnel junction device that adjusts light detection sensitivity by applying a voltage to a gate acting as the light-absorbing part, allowing for external electric field control of the threshold voltage, reducing dependence on doping concentration and enabling auto exposure and electric shutter functions without additional transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a photo diode with small electrostatic capacity is used, then the device area can be reduced, but the photo detector becomes easily saturated with small amounts of light and requires long accumulation time
Solution Approach 1:
The patent changes the fundamental parameter of the light-absorbing part from a photo diode to a tunnel junction device. This device utilizes quantum tunneling effects to achieve high sensitivity with smaller area, resolving the contradiction between reduced device area and maintained photo detection capability. The tunnel junction structure enables efficient charge separation and collection without requiring large accumulation areas.
2Manufacturing precision
If the threshold voltage is determined by doping concentration in manufacturing, then the photoelectric conversion characteristics are fixed, but repetitive manufacturing procedures are required to achieve optimal threshold voltage conditions
Solution Approach 1:
The patent introduces a gate electrode that enables dynamic control of the threshold voltage through applied voltage. This transforms the static threshold voltage determined by fixed doping concentration into a dynamically adjustable parameter, allowing optimal threshold voltage conditions to be achieved without repetitive manufacturing trials. The gate voltage can be tuned to optimize photoelectric conversion characteristics for different application requirements.
3Area of stationary object
If a photo diode with limited photo detection area is used, then the electrostatic capacity is limited, but a relatively long photoelectric charge accumulation time is required to generate minimum electric charge
Solution Approach 1:
The patent changes the detection mechanism from photoelectric effect in a photo diode to quantum tunneling in a tunnel junction device. This parameter change enables significantly improved charge generation efficiency, allowing sufficient electric charge to be generated in the same area much faster. The tunnel junction structure provides enhanced charge separation and reduced recombination losses, reducing the required accumulation time while maintaining small photo detection area.
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 approach enhances sensitivity characteristics, enabling high-sensitivity image sensing in low-light environments and auto exposure adjustments, while simplifying manufacturing and reducing dark current, thus facilitating high-speed video capture.
Implementation Method 1
changes a threshold voltage of a channel using tunneling of electric charge from a floating gate to a source electrode or a drain electrode
Implementation Method 2
When light is incident to the light-absorbing part of the unit pixel of the image sensor, one electron-hole pair (EHP) is generated for one incident photon
Implementation Method 3
adjusting a light detection sensitivity of a photo detector by applying a voltage to a gate which operates as a light-absorbing part to adjust a threshold voltage of a channel
Data Source
AI summary
Disclosed are a photo detector capable of adjusting sensitivity and a unit pixel of an image sensor using the photo detector. The photo detector includes a light-absorbing part that absorbs light; a source and a drain that are separated from the light-absorbing part by an oxide film; a channel that is formed between the source and the drain to generate a flow of electric current between the source and the drain; and a sensitivity adjustment terminal that applies a voltage to the light-absorbing part, in which the light-absorbing part is doped with a first type impurities, the source and the drain are doped with a second type impurities, the flow of electric current in the channel is adjusted based on a change in a quantity of electric charges of the light-absorbing part according to tunneling of an electron excited by the light incident to the light-absorbing part to the source or the drain, and the voltage applied through the sensitivity adjustment terminal is adjusted to adjust a threshold voltage of the channel.