Gas sensors with contact pads
Inventors
Xu, Jennifer • Hunter, Gary W.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-9970914-B1
Publication Date
2018-05-15
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 is a gas sensor designed with multiple layers including a metal layer, a first insulating layer, a conduction path, a contact pad, and a second insulating layer arranged on a substrate. This design enables the metal layer to have distinct sensing and contact areas, where the conduction path electrically connects the metal layer's contact area to the contact pad, and the second insulating layer acts as a diffusion barrier preventing ions from passing through the contact pad to the underlying layers.
The problem being solved arises from prior sensors where direct wire bonding on Schottky diode surfaces compromised sensor integrity, particularly for long-term and high-temperature use, causing deterioration and inconsistent sensor performance. Additionally, electrical connections made directly to the diode were susceptible to substrate defects, physical damage, and affected durability. The challenge was to provide a stable, dependable electrical connection to gas sensors, particularly SiC-based Schottky diodes, without compromising sensor stability or performance.
The invention addresses this by introducing contact pads as intermediates between the electrical connections and the sensitive diode surface. The contact pads, connected to the metal layer by conduction paths through a first insulating layer, allow wire bonding without direct contact with the sensing surface. The second insulating layer on the contact pad further prevents gas ion diffusion, thus protecting the conduction path and metal layer and ensuring more accurate and stable sensing. This multi-layered configuration and fabrication process provide a packaging friendly, robust sensor structure suitable for detecting gases such as hydrogen and hydrocarbons over a wide temperature range.
Claims Coverage
The patent includes one independent claim that defines the key structural and functional features of the sensor incorporating multiple layers and insulating structures to facilitate stable and protected electrical readout connections.
Multi-layer sensor structure with conduction path and insulating layers
The sensor includes a substrate, a metal layer with distinct sensing and contact areas, a first insulating layer that shields the contact area except for a conduction path, a conduction path connecting the metal layer's contact area to a contact pad, and a second insulating layer covering part of the contact pad to prevent diffusion through to the metal layer and conduction path.
Contact pad designed to overlap and electrically connect via conduction path
The contact pad is sized and shaped to overlap the metal layer's contact area and the conduction path, and is thick enough to allow reliable wire bonding, while the conduction path itself is made of conductive material and smaller in area than the first insulating layer.
Diffusion barrier implemented by second insulating layer on contact pad
The second insulating layer covers the portion of the contact pad where it meets the conduction path to form an insulated area that prevents diffusion through the contact pad and conduction path into the metal layer, while leaving another portion exposed for wire bonding electrical connection.
Use of metal oxide barrier layer between substrate and metal layer
A metal oxide layer, such as PdOx, is included between the substrate and metal layer to inhibit chemical reactions that could degrade sensor performance.
Sensor configured as Schottky diode or other semiconductor device
The sensor may be a Schottky diode, capacitor, or transistor with specific material choices such as noble metals (Pt, Pd, etc.) on a silicon carbide substrate with a PdOx barrier interlayer approximately 50 to 200 Angstroms thick.
These inventive features collectively provide a gas sensor structure that enables stable, protected electrical connections through contact pads and insulating layers, avoiding the problems of direct wire bonding on sensitive sensing surfaces and supporting high temperature and long-term gas detection applications.
Stated Advantages
Provides a more stable electrical connection to the sensor metal layer without compromising the sensing surface integrity.
Prevents gas ion diffusion through the contact pad and conduction path, enhancing sensing accuracy.
Enables long-term and high temperature operation by protecting the sensor surface from physical damage and deterioration caused by direct wire bonding.
Allows packaging-friendly sensor design facilitating reliable wire bonding on contact pads rather than direct diode surfaces.
Documented Applications
Hydrogen detection from room temperature to high temperatures.
Hydrocarbon gas detection at elevated temperatures.
Fuel leak detection.
Fire detection.
Engine emission monitoring.
Environmental monitoring.
Fuel cell safety applications.
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