Capacitive Gas Sensor Integrated on ASIC Passivation
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Solution Overview
Problem
Capacitive gas sensors face challenges in miniaturization due to susceptibility to stray capacitances and interference from active circuitry, leading to increased size and cost, as well as sensitivity issues from foreign materials and parasitic coupling.
Innovation Solution
A parallel plate capacitive gas sensor is constructed directly on top of a standard semiconductor ASIC with a thin metal bottom electrode, a gas sensitive layer, and a porous top electrode, where the top electrode overlays the bottom electrode and connects through a via hole to a landing pad, minimizing parasitic coupling and maintaining sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the size of gas sensitive capacitors is reduced to decrease manufacturing cost, then manufacturing cost decreases, but the capacitors become increasingly susceptible to signal degradation from stray capacitances
Solution Approach 1:
The patent merges the gas sensor capacitor with the ASIC substrate by depositing electrodes directly onto the passivation layer of the semiconductor circuit, integrating two previously separate components (sensor and electronics) into a single unified structure, thereby reducing overall size and manufacturing cost while maintaining measurement accuracy through controlled electrode geometry
Solution Approach 2:
The patent introduces a conductive shield layer as an intermediary element between the sensing electrodes and the underlying active circuitry. This shield acts as a mediator that blocks parasitic capacitive coupling from the circuitry while allowing the sensor to function normally, thus preventing signal degradation even in miniaturized configurations
2Area of stationary object
If interdigitated capacitor electrodes are placed directly over active circuitry in the ASIC, then device size decreases, but coupling and interference from the circuitry increases
Solution Approach 1:
A conductive shield layer is positioned between the sensing electrodes and the active circuitry, serving as an intermediary that blocks parasitic capacitive coupling while allowing the compact integration of sensor over circuitry. This shield layer prevents harmful electromagnetic interference from the underlying circuitry affecting the sensor signal
Solution Approach 2:
The patent applies different functional properties to different regions: the area directly over active circuitry is covered with a conductive shield to block interference, while the sensing regions maintain high sensitivity. This local differentiation of properties allows the sensor to be positioned over circuitry without suffering from coupling effects
3Object-affected harmful factors
If a conductive layer is added to shield interdigitated electrodes from circuitry, then interference decreases, but baseline capacitive coupling increases and sensitivity lowers
Solution Approach 1:
The patent transitions from the planar interdigitated electrode configuration to a three-dimensional parallel plate structure with top and bottom electrodes separated by a dielectric layer. This dimensional change allows the sensing capacitor to be positioned directly over circuitry in the vertical dimension while maintaining electrical isolation through the dielectric, thus achieving shielding without increasing baseline capacitance
4Ease of manufacture
If the sensor size is reduced, then manufacturing cost decreases, but parasitic capacitances in interconnections and electronics have greater relative impact
Solution Approach 1:
The sensing capacitor electrodes are directly deposited onto the ASIC substrate, merging the sensor structure with the electronics substrate. This integration eliminates separate interconnection elements and reduces the length of parasitic capacitance paths, thereby minimizing their relative impact even in miniaturized sensors
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 allows for a compact, cost-effective gas sensor with reduced parasitic capacitance and improved sensitivity, while maintaining accuracy and reliability by ensuring consistent capacitance and minimizing interference from underlying circuitry.
Implementation Method 1
changing gas concentration changes the dielectric constant of the gas sensitive material and changes the capacitance of the parallel plate capacitor
Implementation Method 2
a top electrode comprised of a highly porous conducting polymer that allows the diffusion of the selected gas through the electrode and into the gas sensitive material
Implementation Method 3
The capacitance of a capacitive gas sensor is a function of gas concentration, and the capacitance is measured by associated electronics capable of exciting the sensor electrically
Data Source
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AI summary
There is disclosed a capacitive sensor on a passivation layer of a semiconductor circuit such as an ASIC, and a method for manufacturing such sensor. The system and method may comprise: forming a bottom electrode layer and landing pad (520) on a portion of the passivation layer located over active circuitry of the ASIC; forming a gas sensitive layer (530) onto the bottom electrode layer and the landing pad; creating a via (540) through the gas sensitive layer to expose a portion of the landing pad; forming a top electrode layer (550) onto the gas sensitive layer, wherein the top electrode layer completely overlays a surface area of the bottom electrode layer, and wherein the forming process for the top electrode layer deposits a portion of the top electrode layer into the via hole, thereby forming an electrical connection between the top electrode layer and the landing pad.