Gas sensors with contact pads
Inventors
Xu, Jennifer • Hunter, Gary W.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-10732161-B2
Publication Date
2020-08-04
Expiration Date
2035-04-06
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Abstract
Systems, methods, and other embodiments associated with gas detecting sensors. According to one embodiment, a gas sensor includes a metal layer, a barrier interlayer, a substrate layer, a first insulating layer, a conduction path, a contact pad, and a second insulating layer. The conduction path connects the metal layer to the contact pad. The second insulating layer prevents diffusion through the contact pad, the conduction path, or the metal layer. The sensor includes a wire bonded electrical connection to the contact pad such that voltage can be determined and/or applied.
Core Innovation
The invention described relates to gas detecting sensors employing a microfabricated, miniaturized Schottky diode structure with contact pads to improve electrical connection stability. The sensor comprises a substrate, a metal layer, a first insulating layer with a conduction path, a contact pad, and a second insulating layer. This structure allows an electrical connection to be made to the contact pad rather than directly to the diode's sensing surface, thereby preventing degradation of sensor performance during wire bonding and prolonged high temperature operation.
The problem addressed by this invention stems from deficiencies in prior silicon carbide (SiC) based Schottky diode gas sensors, where wire bonding was performed directly on the diode surface. Such direct bonding compromised the integrity of the sensor surface, especially under long-term high temperature conditions, leading to changes or deterioration of the sensing surface and inconsistent sensor performance. Furthermore, direct electrical connections to the diode were susceptible to substrate defects and could physically damage the sensor. The invention resolves these issues by introducing contact pads and insulating layers to provide a stable, durable electrical interface that preserves the sensing area's integrity.
Claims Coverage
There are two independent claims presenting inventive features related to methods of fabricating gas sensors with contact pads that improve sensor durability and electrical connection stability.
Method for fabricating gas sensor with contact pad and insulating layers
The method includes depositing a metal layer on a substrate having both a sensing area and a contact area, applying a first insulating layer covering substantially the entire contact area but leaving a conduction path open, depositing a contact pad overlapping the conduction path, and then depositing a second insulating layer overlapping the conduction path on the contact pad. This insulating layering prevents gas ion diffusion into the contact area and metal layer while allowing reliable electrical connection.
Method for forming conduction path and contact pad as a single body on sensor
Starting from a substrate with metal oxide and metal layers shaped with sensing and contact areas, the method deposits a first insulating layer with an opening, fills the opening and forms a contact pad by depositing conductive material, and finally deposits a second insulating layer overlapping the conduction path. The contact pad substantially overlaps the first insulating layer and includes an insulated portion covered by the second insulating layer and an exposed portion to allow electrical connection to a voltage source.
Both independent claims focus on fabricating a gas sensor featuring a metal layer on a substrate, first and second insulating layers that provide a diffusion barrier over the contact area and conduction path, and a contact pad electrically connected via a conduction path. These features enable stable wire bonding away from the sensing area, preventing sensor degradation and improving electrical connection reliability.
Stated Advantages
The sensor structure ensures a more stable electrical connection that does not degrade the quality or performance of the sensor.
The second insulating layer acts as a diffusion barrier preventing gas ions from diffusing into the conduction path, contact pad, or metal layer, improving sensing accuracy.
The contact pad design protects the metal layer from damage such as burnout caused by electrical connection overheating, especially during wire bonding.
The design supports high temperature stable sensing, enabling sensing at elevated temperatures up to at least 600° C.
Wire bonding to the contact pad rather than directly on the diode preserves the integrity of the sensor surface for long term and repeatable sensor performance.
Documented Applications
Detection of hydrogen and hydrocarbon gases at temperatures ranging from room temperature to high elevated temperatures up to 600° C.
Fuel leak detection.
Fire detection.
Engine emission monitoring.
Environmental monitoring.
Fuel cell safety applications.
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