Stacked Pixel Sensor Layout for Larger Photon Collection Area
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Solution Overview
Problem
As the size of pixel sensors in CMOS image sensors decreases, the available area for photon collection also decreases, leading to reduced light sensitivity and contrast.
Innovation Solution
Incorporating one or more transistors of a pixel sensor, such as a source follower transistor, a row select transistor, and a transfer transistor, on a circuitry die instead of the sensor die, allowing for a larger area for photon collection by reducing the transistor area on the sensor die.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If transistors are integrated on the sensor die with pixel sensors, then device complexity is reduced and integration is improved, but the area available for photon collection decreases
Solution Approach 1:
The patent moves transistors from the two-dimensional plane of the sensor die to a third dimension by stacking them on a separate circuitry die, which is then bonded to the sensor die. This vertical separation allows the photodiode on the sensor die to occupy maximum area for photon collection while transistors reside on the circuitry die, resolving the area conflict through spatial reorganization in three dimensions.
Solution Approach 2:
The pixel sensor is divided into two functional segments: the photodiode portion remains on the sensor die to maximize light-sensitive area, while the transistor portion is separated and placed on a dedicated circuitry die. This segmentation allows each component to be optimized independently for its specific function without compromising the other.
2Productivity
If pixel sensor size is decreased, then productivity and pixel density are improved, but light sensitivity and contrast deteriorate
Solution Approach 1:
By relocating transistors to a separate circuitry die and bonding it to the sensor die, the patent frees up significant area on the sensor die. This additional area can be allocated to enlarge the photodiode area within each pixel sensor, thereby improving light sensitivity and contrast even as pixel density increases through smaller pixel pitch.
Solution Approach 2:
The circuitry die serves multiple functions: it houses all transistor operations for the pixel sensors, provides signal processing capabilities, and enables high-density interconnect routing. This multi-functional integration on the circuitry die allows the sensor die to be dedicated primarily to photon collection, improving sensitivity while maintaining high pixel density.
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 increases the area for photon collection, enabling smaller pixel sensor sizes while maintaining or improving light sensitivity and contrast, which is beneficial for mobility and small form factor applications.
Implementation Method 1
a photodiode configured to convert photons of incident light into a photocurrent of electrons
Data Source
AI summary
Some implementations described herein provide pixel sensor configurations and methods of forming the same. In some implementations, one or more transistors of a pixel sensor are included on a circuitry die (e.g., an application specific integrated circuit (ASIC) die or another type of circuitry die) of an image sensor device. The one or more transistors may include a source follower transistor, a row select transistor, and/or another transistor that is used to control the operation of the pixel sensor. Including the one or more transistors of the pixel sensor (and other pixel sensors of the image sensor device) on the circuitry die reduces the area occupied by transistors in the pixel sensor on the sensor die. This enables the area for photon collection in the pixel sensor to be increased.