Elongated Contacts for Image Sensor Readout Circuit Footprint Reduction
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Solution Overview
Problem
Current solid-state image sensors, such as CMOS image sensors, do not effectively utilize electrical charge accumulated during idle periods, as it is not measured or used to generate an image.
Innovation Solution
The proposed solution involves a semiconductor device with a cluster of pixels and a readout circuit that includes a reset transistor, a source follower transistor, and a row select transistor, where elongated contacts are used to reduce the footprint and increase the efficiency of the readout process, allowing for the measurement and utilization of electrical charge accumulated during both integration and idle periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional readout circuit configuration is used, then the circuit can perform basic readout function, but the footprint is large and spacing between components is reduced
Solution Approach 1:
The contact structure is extended in the vertical dimension by forming elongated contacts that penetrate through multiple dielectric layers and contact different components at different heights. This vertical extension allows the readout circuit to maintain adequate horizontal spacing between components while reducing the overall footprint area.
Solution Approach 2:
The elongated contact structure is nested within the vertical stack of dielectric layers, with the contact penetrating through multiple layers and contacting different components at different levels. This nesting approach allows multiple connections to be achieved within a compact vertical space, reducing the horizontal footprint.
2Object-affected harmful factors
If component spacing is increased to reduce interference, then the readout circuit footprint increases
Solution Approach 1:
By transitioning to vertical connections through elongated contacts, the design achieves component isolation in the horizontal plane while maintaining compact footprint. The harmful interference is reduced through increased horizontal spacing, and the vertical dimension compensates for the reduced footprint area.
3Area of stationary object
If elongated contacts are used to reduce footprint, then contact resistance may increase
Solution Approach 1:
The elongated contact structure merges multiple contact functions into a single continuous conductive path that penetrates through multiple dielectric layers. This unified structure reduces the number of separate contact interfaces, thereby reducing cumulative contact resistance while achieving footprint reduction.
Solution Approach 2:
The elongated contact serves multiple functions simultaneously: it provides electrical connection through multiple layers, acts as a spacer maintaining horizontal distances, and reduces the overall footprint. This multi-functionality allows footprint reduction without compromising electrical performance.
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 enables the efficient measurement and utilization of electrical charge during idle periods, improving the image generation process by enhancing the readout efficiency and reducing the footprint of the readout circuit.
Implementation Method 1
When a pixel array of the solid-state image sensor is exposed to light, photosensitive sensors of the pixel array convert the light into voltage
Data Source
AI summary
An image sensor includes a photosensitive sensor, a floating diffusion node, a reset transistor, and a source follower transistor. The reset transistor comprises a first source/drain coupled to the floating diffusion node and a second source/drain coupled to a first voltage source. The source follower transistor comprises a gate coupled to the floating diffusion node and a first source/drain coupled to the second source/drain of the reset transistor. A first elongated contact contacts the second source/drain of the reset transistor and the first source/drain of the source follower transistor. The first elongated contact has a first dimension in a horizontal cross-section and a second dimension in the horizontal cross-section. The second dimension is perpendicular to the first dimension, and the second dimension is less than the first dimension.