Capacitive Fingerprint Sensor Electrostatic Lens
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Solution Overview
Problem
Capacitive fingerprint sensors in consumer electronics face challenges due to space constraints, leading to increased separation between the contact surface and the array of capacitive sensing elements, which results in blurring of the electric field and reduced resolution.
Innovation Solution
Incorporating an electrostatic lens within the dielectric structure, composed of patterned conductive layers, to shape the electric field and improve resolution by adjusting the relative voltage of these layers to optimize image sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the separation between the contact surface and the array of capacitive sensing elements is increased to accommodate other components (such as display stacks and touch screens), then more components can be integrated into the device, but the resolution of the fingerprint sensor deteriorates due to blurring of the electric field
Solution Approach 1:
An electrostatic lens is introduced as an intermediary component between the contact surface and the capacitive sensing elements. This lens focuses the electric field lines, compensating for the blurring effect caused by increased separation distance. The lens consists of conductive structures that manipulate the electric field distribution, allowing the sensor to maintain high resolution despite the larger gap required for integrating display stacks and touch screens.
2Volume of stationary object
If the separation between the contact surface and the array of capacitive sensing elements is increased, then space for other components is available, but the electric field becomes blurred resulting in reduced resolution
Solution Approach 1:
The electrostatic lens changes the parameters of the electric field by focusing it. By adjusting the voltage applied to the conductive structures of the lens, the focal point of the electric field can be controlled to coincide with the capacitive sensing elements. This parameter control allows the system to maintain detection resolution even when the physical separation distance is increased to provide space for other components.
3Area of stationary object
If capacitive sensing elements are placed behind display stacks and touch screens, then surface space is optimized, but the opacity of the sensing elements and separation distance reduce image quality
Solution Approach 1:
The electrostatic lens serves as a mediator that compensates for the degradation caused by the display stack and touch screen layers. By focusing the electric field through these intermediate layers, the lens ensures that sufficient signal strength and resolution are maintained at the capacitive sensing elements, enabling high-quality fingerprint imaging even when the sensor is positioned behind multiple device layers.
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
The electrostatic lens effectively reduces blurring and enhances the resolution of fingerprint images, allowing for effective image sensing with increased separation between the contact surface and the capacitive sensing elements, thereby improving design options in consumer electronic devices.
Implementation Method 1
an electrostatic lens formed within the dielectric structure
Implementation Method 2
shape the electric field and improve resolution
Data Source
AI summary
A capacitive fingerprint sensor, including: a dielectric structure having a contact surface and a sensor surface; an array of capacitive sensing elements held on or near the sensor surface of the dielectric structure; and an electrostatic lens formed within the dielectric structure.