General Electric Granted GaN And SiC Sensor Patent
A GaN sensor looks set to surpass current methods for monitoring faults in oil-filled transformers, if the patent granted to General Electric on August 14 is true to its claims.
GE originally filed the patent on December 13, 2002, based on research performed at its Global Research Center in Niskayuna, New York, and its sister site in Pointe-Claire, Canada.
Since then, the group has also published its results in physica status solidi (c), demonstrating a hardier technology than previous tin dioxide and silicon-based approaches.
Mass-producible though they may be, the existing technologies are sensitive to temperature fluctuations typical to the outdoor location of many transformers. Temperature changes can affect sensor accuracy and often render silicon devices ineffective.
By contrast, GE asserts that it can make a detector based on Schottky diodes and FETs, made from GaN and SiC, which provide stable responses up to 450 deg C, over a wide range of pressures.
Impending or existing faults in oil-filled electrical equipment, from arcing to overheating, may be detected through the corresponding generation of undesirable gases.
In GE s sensor, an electrical field is induced at the surface of the device by gas molecules containing hydrogen, adsorbed onto a metallic gate electrode, and catalytically dissociated.
The resulting atomic hydrogen diffuses through the gate and forms a dipole layer at the semiconductor surface, electrically altering the Schottky barrier height at the Schottky/GaN interface.
Applying an electric field across the diode allows quantitative monitoring, by holding either the current or voltage constant and measuring the change in the variable parameter.
Coupling the diode with a FET amplifies the sensitivity of the sensor, and a SiN passivation layer helps filter out larger molecules, reducing further the development of surface states "“ an already infrequent occurrence given the slow oxidation of GaN and SiC.
GE has not widely discussed its plans for this technology, however it is clearly well positioned to validate the possible applications, given the wide range of transformers it sells, and its veteran status in the energy industry.