MIM Storage Layer for Compact High-Dynamic-Range Image Sensors
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Solution Overview
Problem
Existing image sensors face challenges in achieving a compact, high dynamic range, and high sensitivity to motion, particularly in color image sensors with red, green, and blue photosensors, where miniaturization reduces photocharge storage capacity and dynamic range.
Innovation Solution
The image sensor design includes a photosensor layer with conventional and EVS photosensors, a storage layer with metal-insulator-metal (MIM) storage elements, and a signal processing layer. The MIM storage elements are electrically connected in series between the photosensors and the signal processing circuitry, increasing photocharge storage capacity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If image sensors are miniaturized to achieve compact form factor, then device size is reduced, but photocharge storage capacity and dynamic range decrease
Solution Approach 1:
The patent implements a nested structure where MIM storage elements are integrated within the image sensor device. The storage elements are positioned between the photosensor array and readout circuitry, nesting the storage function within the existing device architecture. This allows increased photocharge storage capacity without proportionally increasing the overall device volume, effectively resolving the contradiction between compact size and storage capacity.
Solution Approach 2:
The patent transitions from two-dimensional photosensor arrays to three-dimensional MIM storage elements. The MIM structure utilizes vertical stacking of metal-insulator-metal layers, adding a dimensional aspect that increases storage capacity without expanding the lateral footprint. This dimensional change enables higher photocharge storage in a compact form factor.
2Reliability
If photocharge storage capacity is increased to improve dynamic range, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The MIM storage elements serve multiple functions within the image sensor: they provide photocharge storage capacity enhancement, act as charge transfer intermediaries between photosensors and readout circuitry, and maintain compatibility with existing CMOS fabrication processes. This multi-functionality increases dynamic range without proportionally increasing device complexity, as a single structure accomplishes multiple objectives.
Solution Approach 2:
The patent utilizes parameter changes in the MIM capacitor structure, specifically varying the insulator layer thickness and metal layer configurations, to optimize storage capacity while maintaining fabrication simplicity. By adjusting these parameters during standard CMOS processing, the device achieves enhanced dynamic range without requiring fundamentally new manufacturing steps or complex device architectures.
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 design enhances the dynamic range and sensitivity to motion of image sensors by increasing photocharge storage capacity, allowing for more efficient light detection and processing, while maintaining a compact form factor.
Implementation Method 1
metal-insulator-metal (MIM) storage elements having first terminals electrically connected with the photosensors of the photosensor wafer and second terminals electrically connected with the signal processing circuitry of the signal processing wafer
Data Source
AI summary
In a method of fabricating an image sensor, a photosensor wafer is formed, comprising an array of photosensors. A signal processing wafer is formed, comprising signal processing circuitry configured to receive and process photocharge collected by the photosensors of the photosensor wafer. A storage wafer is formed, comprising metal-insulator-metal (MIM) storage elements. The photosensor wafer is secured to a first side of the storage wafer, thereby electrically connecting the photosensors of the photosensor wafer and MIM storage elements of the storage wafer. The signal processing wafer is secured to a second side of the storage wafer, thereby electrically connecting the MIM storage elements of the storage wafer with the signal processing circuitry of the signal processing wafer.