Stacked Image Sensor Substrates for Source Follower Performance
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Solution Overview
Problem
Solid-state image pickup devices face challenges when circuit elements are formed on substrates other than {100} substrates, such as {111} substrates, resulting in poor characteristics.
Innovation Solution
A solid-state image pickup device is designed with a {111} substrate as the first substrate, incorporating a photoelectric conversion unit, a lens, and a transistor in a source follower circuit on substrates with different crystal planes, including a {100} or {110} substrate for the transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a {111} substrate is used for the first substrate, then it is easy to form vertical trenches and horizontal trenches by etching, but the characteristics of the source follower circuit deteriorate
Solution Approach 1:
The device is divided into multiple substrates with different crystal planes. The first substrate uses {111} orientation for easy trench formation, while the second substrate uses {100} or other orientations for forming the source follower circuit transistor, separating the conflicting requirements into different physical locations.
Solution Approach 2:
The solution moves from a single-substrate approach to a multi-substrate stacked architecture. By adding the dimension of vertical stacking with different substrate orientations, the patent resolves the contradiction by allowing each substrate to optimize for its specific function without compromise.
2Productivity
If a substrate other than {100} is used, then etching of vertical and horizontal trenches becomes easier, but circuit element characteristics become poor
Solution Approach 1:
Different regions of the device use substrates with different crystal plane orientations optimized for their specific functions. The {111} substrate region is optimized for trench etching, while the {100} substrate region is optimized for circuit element performance, allowing each local area to have the quality needed for its purpose.
Data Source
AI summary
Provided is a solid-state image pickup device that includes a first substrate that is a substrate other than a {100} substrate, a photoelectric conversion unit that is provided in the first substrate, a lens that is provided above the first substrate, one or more substrates that are provided below the first substrate and have a crystal plane different from a crystal plane of the first substrate, and a transistor that is provided on an upper surface or a lower surface of one of the one or more substrates and is included in a source follower circuit.