Photo-JFET Retinal Pixels for High-Acuity Neural Stimulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional retinal prostheses face limitations in achieving high visual acuity due to the tradeoff between pixel size and photocurrent required for neural stimulation, with existing technologies struggling to efficiently convert natural light into electrical current for stimulation.
Innovation Solution
The development of a vertically integrated photosensitive junction field-effect-transistor (Photo-JFET) that integrates a photodetector, amplifier, and neural electrode stimulator within a single silicon pixel mesa, enabling gain without sacrificing fill factor and allowing for scaling of pixel size down to 10-20 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photodiodes are used to convert light into electrical currents for neural stimulation, then visual information can be transduced, but the intensity of light under typical natural retinal irradiance is orders of magnitude too low to be efficiently converted into electrical current for neural stimulation
Solution Approach 1:
The patent combines a photodiode with a CMOS amplifier circuit within each pixel to create an integrated photo-sensing unit. This merging allows the photodiode to convert light into photocurrent while the integrated amplifier boosts the signal to sufficient levels for neural stimulation, resolving the inefficiency of standalone photodiodes under natural retinal irradiance conditions
Solution Approach 2:
The patent introduces an intermediary CMOS amplifier circuit between the photodiode and the neural stimulation electrodes. This intermediary component amplifies the weak photocurrent generated by the photodiode, enabling efficient conversion of low-intensity light into sufficient electrical current for reliable neural stimulation
2Device complexity
If an external light source in the NIR wavelength is used to power and control the current produced by the photodiode array, then the form factor of the implanted hardware can be simplified, but the high intensity of irradiating NIR light and the relatively large pixel area required limit the resolution
Solution Approach 1:
The patent transitions from relying on external optical addressing to an electronically controlled solution where each pixel contains its own amplifier circuit. This dimensional shift from optical to electronic control enables smaller pixel sizes and higher resolution without requiring high-intensity NIR irradiation, while maintaining simplified hardware form factor
3Manufacturing precision
If the pixel area is reduced to increase prosthesis resolution, then visual acuity can be improved, but the photocurrent produced becomes insufficient to drive neural stimulation
Solution Approach 1:
The patent merges a photodiode with an integrated CMOS amplifier within each pixel. This combination allows smaller pixel areas to maintain sufficient photocurrent output for neural stimulation, as the integrated amplifier compensates for the reduced light-collecting area, enabling high resolution without sacrificing stimulation capability
Solution Approach 2:
The patent changes the operational parameters of the photodiode by integrating it with an amplifier circuit that actively compensates for reduced photocurrent. This parameter change enables small pixels to produce sufficient stimulation current through electronic gain rather than relying solely on larger optical collection area
4Ease of operation
If a CMOS amplifier circuit is integrated within each pixel to amplify the primary photocurrent, then spatiotemporal contrast can be encoded without externally worn imaging components, but the complexity of the required hardware increases and limits the fill factor
Solution Approach 1:
The patent segments the retinal prosthesis into pixelated units, with each pixel containing an integrated photodiode-amplifier combination. This segmentation enables distributed spatiotemporal contrast encoding across the array while maintaining manageable complexity at each pixel level, and the modular design facilitates efficient packing to maximize fill factor
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 approach enables the production of a broad range of currents (0.1-100 μA) for robust retinal neural stimulation within a safe range of NIR irradiance, potentially restoring high acuity vision with a prosthetic visual acuity of around 20/60.
Implementation Method 1
A vertically integrated photosensitive junction field-effect-transistor (Photo-JFET) that combines a photodetector, amplifier, and neural electrode stimulator within a single silicon pixel mesa
Implementation Method 2
A vertically integrated photosensitive junction field-effect-transistor (Photo-JFET) that combines a photodetector, amplifier, and neural electrode stimulator within a single silicon pixel mesa, enabling gain without sacrificing fill factor
Data Source
AI summary
Optoelectronic retinal prostheses transduce light into electrical current for neural stimulation. A novel optoelectronic pixel architecture is presented comprising a vertically integrated photo junction field-effect-transistor (Photo-JFET) and neural stimulating electrode. Experimental measurements demonstrate that optically addressed Photo-JFET pixels utilize phototransistive gain to produce a broad range of neural stimulation current and can effectively stimulate retinal neurons in vitro. The compact nature of the Photo-JFET pixel can enable high resolution retinal prostheses with a theoretical visual acuity ˜20/60 to help restore vision in patients with degenerative retinal diseases.