Stacked Image Sensor Pad Protection Circuit for Noise Isolation
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Solution Overview
Problem
In solid-state imaging devices, finer pixels lead to reduced light sensitivity due to smaller light-receiving areas of photoelectric conversion elements, and direct connection of input/output pads to the circuit introduces external noise, causing malfunctions and affecting image signals.
Innovation Solution
A solid-state imaging device design where a protection circuit is integrated on the second semiconductor substrate, electrically connected to the pad and peripheral circuit, mitigating external noise and protecting the circuit and photoelectric conversion element from noise ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixels are made finer to obtain high definition image, then image definition is improved, but light receiving area of photoelectric conversion element is reduced resulting in reduced sensitivity
Solution Approach 1:
The invention divides the semiconductor substrate into two separate substrates: a first substrate containing photoelectric conversion elements and a second substrate containing peripheral circuits. This segmentation allows independent optimization of each substrate - the first substrate can have larger photoelectric conversion elements for better light sensitivity while the second substrate handles the circuit functions, thus resolving the contradiction between fine pixel definition and light receiving area.
2Device complexity
If input/output pad is directly connected to circuit of first substrate, then connection is simplified, but external noise is imparted to circuit causing malfunction
Solution Approach 1:
The invention introduces a second substrate as an intermediary layer between the input/output pad and the circuit of the first substrate. This second substrate contains a connection portion that electrically connects the pad to the peripheral circuit while providing noise shielding. The intermediary substrate acts as a barrier that prevents external noise from directly reaching the sensitive circuit, thus resolving the contradiction between simple connection and noise protection.
3Ease of manufacture
If input/output pad is formed after connection portion is exposed by polishing, then pad formation is simplified, but external noise can be incorporated into photoelectric conversion element
Solution Approach 1:
The invention performs preliminary action by forming the connection portion that extends through the second substrate before the input/output pad is formed. This pre-formed connection structure with inherent noise shielding capability is established in advance, so when the pad is later formed by exposing the connection portion through polishing, the noise protection is already in place. This resolves the contradiction by preparing the noise barrier beforehand while maintaining simple pad formation process.
Data Source
AI summary
A solid-state imaging device includes: a first semiconductor substrate including a photoelectric conversion element; and a second semiconductor substrate including at least a part of a peripheral circuit arranged in a main face of the second semiconductor substrate, the peripheral circuit generating a signal based on the charge of the photoelectric conversion element, a main face of the first semiconductor substrate and the main face of the second semiconductor substrate being opposed to each other with sandwiching a wiring structure therebetween; a pad to be connected to an external terminal; and a protection circuit electrically connected to the pad and to the peripheral circuit, wherein the protection circuit is arranged in the main face of the second semiconductor substrate.