Backside Imaging Sensor Layout for Sensitivity and Ground Stability
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Solution Overview
Problem
Monolithic CCD-CMOS sensors face challenges in increasing processing speed due to increased current consumption and ground potential fluctuations, which affect signal processing and noise in the output signal, especially when thinning substrates for backside illumination.
Innovation Solution
A backside incident-type imaging element with a semiconductor substrate having a thicker region for the analog-digital converter and a thinner region for the light receiving portion, with a recess on the back surface to gradually increase thickness, allowing for improved light sensitivity and stabilization of the ground potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the substrate is thinned to enable backside illumination, then light sensitivity is improved, but ground potential stability deteriorates due to increased resistance
Solution Approach 1:
The substrate thickness is made non-uniform, with a first region (under light receiving portions) being thinner to improve light sensitivity and a second region (under signal processing circuits) being thicker to provide low resistance ground potential. This local differentiation allows each region to have the thickness property optimal for its function.
Solution Approach 2:
The substrate is divided into multiple regions with different thickness characteristics: a first region for light reception optimized for light penetration, and a second region for signal processing optimized for electrical grounding. This segmentation allows simultaneous optimization of optical and electrical performance.
2Productivity
If processing speed is increased, then productivity is improved, but current consumption increases causing ground potential fluctuations
Solution Approach 1:
The thicker second region provides low resistance grounding specifically for signal processing circuits, enabling high-speed operation with increased current consumption without causing ground potential fluctuations that would affect signal quality.
3Ease of manufacture
If uniform substrate thinning is applied, then manufacturing simplicity is maintained, but both light sensitivity and ground stability cannot be optimized simultaneously
Solution Approach 1:
Instead of uniform thinning, the substrate is processed to have different thicknesses in different regions, allowing simultaneous optimization of light sensitivity (thin region) and ground stability (thick region) while using standard semiconductor manufacturing techniques.
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 processing speed while maintaining high sensitivity and stabilizing the ground potential, reducing noise and current consumption, thus improving the overall performance of the imaging element.
Implementation Method 1
a light receiving portion configured to generate a signal charge according to incident light from a side of the back surface
Data Source
AI summary
A backside incident-type imaging element includes a semiconductor substrate having a front surface and a back surface on an opposite side from the front surface, a ground potential being applied to the semiconductor substrate, and a semiconductor layer formed on the front surface, in which the semiconductor layer has a first element part that includes a light receiving portion generating a signal charge according to incident light from a side of the back surface and outputs a signal voltage corresponding to the signal charge, and a second element part that includes an analog-digital converter converting the signal voltage output from the first element part into a digital signal.