Charge Modulation Element for Uniform Electric Field in TOF Sensors
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Solution Overview
Problem
Existing charge-modulation elements in TOF range sensors face issues with noise and dark current generation due to interface defects and interface states, leading to difficulties in maintaining a uniform electric field over long charge transport paths, which affects the speed and symmetry of signal charge transport.
Innovation Solution
A charge-modulation element with a triple-output structure, featuring a pixel constructing area with symmetrically arranged charge-accumulation regions and field-control electrodes, uses periodic field-control pulses to establish potential gradients, facilitating the transport of signal charges along H-shaped or X-shaped charge transport paths, thereby controlling the electric field and reducing noise and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a long charge transport path is used in existing charge-modulation elements, then the transport distance is extended, but the electric field uniformity deteriorates and noise/dark current increases due to interface defects
Solution Approach 1:
The charge transport path is segmented into multiple regions with different impurity concentrations (first conductivity type and second conductivity type regions alternating). This segmentation creates multiple depletion regions that collectively maintain electric field uniformity over the extended transport distance, preventing carrier stopping while avoiding interface defect accumulation at single boundaries
Solution Approach 2:
Different regions along the charge transport path are assigned different impurity concentrations to create locally optimized electric fields. The alternating high and low impurity concentration regions provide locally controlled depletion zones that maintain overall field uniformity across the long transport path, addressing the uniformity issue without requiring the entire path to have identical properties
2Length of stationary object
If a long charge transport path is used, then the transport distance is extended, but the transport speed deteriorates due to difficulty in maintaining uniform electric field
Solution Approach 1:
The transport path is divided into alternating regions of high and low impurity concentration, creating a series of depletion regions that collectively provide sustained electric field strength over long distances. This segmented approach maintains transport speed by ensuring adequate field strength throughout the extended path without requiring a single uniformly high-field region
Solution Approach 2:
The impurity concentration parameter is varied periodically along the charge transport path to modulate the electric field strength. By changing the impurity concentration from high to low and back, the patent creates alternating depletion regions that maintain appropriate field strength for fast transport over extended distances
3Reliability
If field-control electrodes are added to maintain uniform electric field, then the electric field control is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the field control function from separate electrodes and integrates it directly into the semiconductor structure through alternating doped and undoped regions. The impurity concentration variations themselves act as the field-control mechanism, eliminating the need for additional field-control electrodes and reducing device complexity
Solution Approach 2:
The semiconductor structure itself provides the electric field control function through its internal impurity concentration distribution. The alternating high and low impurity regions automatically create the necessary depletion regions and electric fields without requiring external control electrodes, making the structure self-regulating
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 solution enables higher-speed, symmetric transport of signal charges over long distances, reducing noise and dark current issues, resulting in a solid-state imaging device with lower noise, higher resolution, and faster response times.
Implementation Method 1
a pinning layer 34 of a first conductivity type being in contact with a surface of the surface buried region 35
Implementation Method 2
a first field-control electrode pair (41a, 41b)... provided on the insulating film 11 at positions surrounding the light-receiving area... Depletion potentials of a surface buried region 35 are sequentially changed by periodically applying field-control pulses...
Implementation Method 3
facilitating control of potential distribution so as to maintain a substantially uniform electric field over a long distance of the charge transport path... transport signal charges to a plurality of target regions, through long charge transport paths at a higher speed
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
Provided are a charge-modulation element easily enabling an electric field to be uniform over a long distance of a charge transport path and avoiding problems caused by interface defects, and a solid-state imaging device. The charge-modulation element includes a first charge-accumulation region (61), a second charge-accumulation region (62), a third charge-accumulation region (63), and a fourth charge-accumulation region (64), provided symmetric with respect to a center position of a light-receiving area, and a first field-control electrode pair (41a, 41b), a second field-control electrode pair (42a, 42b), a third field-control electrode pair (43a, 43b), and a fourth field-control electrode pair (44a, 44b), arranged on both sides of respective charge transport paths, for changing depletion potentials of the charge transport paths, which extend from the center position of the light-receiving area to the first charge-accumulation region (61), the second charge-accumulation region (62), the third charge-accumulation region (63), and the fourth charge-accumulation region (64).