Image Sensor Gate with Segmented Dielectric for Reduced Capacitance
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Solution Overview
Problem
Conventional CMOS image sensors suffer from low efficiency due to charge loss during signal charge transfer and slow readout speed caused by high gate to doped semiconductor region capacitance.
Innovation Solution
The design includes a semiconductor substrate with a gate having a dielectric layer with a thinner first section and a thicker second section, a photodiode beneath the gate, and doped semiconductor regions to reduce capacitance and enhance charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional gate structure is used in CMOS image sensor, then the device is simpler to manufacture, but the gate to doped semiconductor region capacitance is high causing slow readout speed
Solution Approach 1:
The gate dielectric layer is segmented into two distinct sections: a first section over the photodiode and a second section over the doped semiconductor region. The second section has a greater thickness than the first section, creating a capacitive divider effect that reduces the effective gate-to-doped region capacitance and enables faster readout speeds while maintaining manufacturability through standard multi-layer dielectric processes
Solution Approach 2:
Different sections of the gate dielectric layer are assigned different thicknesses to optimize local functions: the thinner first section maintains strong field coupling for efficient charge collection from the photodiode, while the thicker second section reduces parasitic capacitance to the doped semiconductor region, thereby improving readout speed without compromising charge transfer efficiency
2Reliability
If signal charge is transferred through conventional gate structure, then the process is simpler, but charge loss occurs during transfer reducing detection efficiency
Solution Approach 1:
The gate dielectric is divided into two sections with different thicknesses to create distinct electrical field regions. This segmentation allows the gate to simultaneously perform charge collection from the photodiode through the thinner first section while minimizing charge loss to the doped semiconductor region through the thicker second section, thereby improving signal detection efficiency
Solution Approach 2:
The gate structure with differential dielectric thickness acts as an intermediary between the photodiode and the doped semiconductor region. It mediates the charge transfer process by providing a controlled capacitive coupling that directs signal charges to the photodiode while blocking excess charges from being lost to the doped region, thus preventing charge loss during transfer
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 results in lower gate to doped semiconductor region capacitance, faster readout speed, and improved signal detection efficiency by preventing charge loss during signal transfer.
Implementation Method 1
incident photons are detected by a pinned photodiode (PPD). The photons incident on a PPD generates a signal charge
Implementation Method 2
charge transfer of the signal charge... gate to doped semiconductor region capacitance
Data Source
AI summary
An image sensor pixel comprises a semiconductor substrate and a gate having a dielectric layer with a first section and a second section over the semiconductor substrate. The first section of the dielectric layer is thinner than the second section. A photodiode is disposed substantially beneath the gate. A gate well region is disposed beneath the gate and overlying the photodiode. A first doped semiconductor region separates the gate well region from a second doped semiconductor region. The second doped semiconductor region is in the semiconductor substrate and is adjacent to the gate.