Wolfspeed has been granted a patent for a transistor design that reduces switching losses in bidirectional conduction applications. The transistor includes a substrate, a drift layer, a junction implant, a source contact, a drain contact, a gate insulator, and a gate contact. The softness factor of the body diode in the transistor is greater than 0.5, resulting in improved switching performance and reduced losses. GlobalData’s report on Wolfspeed gives a 360-degree view of the company including its patenting strategy. Buy the report here.
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According to GlobalData’s company profile on Wolfspeed, Quantum dot devices was a key innovation area identified from patents. Wolfspeed's grant share as of September 2023 was 64%. Grant share is based on the ratio of number of grants to total number of patents.
Transistor with improved body diode softness factor
A recently granted patent (Publication Number: US11769827B2) describes a novel transistor design with improved performance characteristics. The transistor includes a substrate with a specific doping type and concentration, and a drift layer on top of the substrate with the same doping type but a different doping concentration. A junction implant is present in the drift layer, consisting of a body well with a doping type opposite to that of the substrate and a specific doping concentration, and a source well within the body well with the same doping type as the substrate. The transistor also features a source contact in electrical contact with the source well and body well, a drain contact in electrical contact with the substrate, a gate insulator, and a gate contact on the gate insulator.
One of the key aspects of this transistor design is the inclusion of a body diode between the source contact and the drain contact. The body diode is configured to have a specific concentration of minority carriers at the interface between the body well and the drift layer during forward bias operation. Additionally, the transistor includes a recombination region below the body well, which has a higher concentration of recombination centers compared to the drift layer. This recombination region is created through ion implantation, potentially using argon.
The patent also highlights that the substrate and drift layer can be made of silicon carbide, and the body diode is a non-punch through diode. The breakdown voltage of the transistor is specified to be between 350V and 20 kV, while the on-state resistance is between 0.3 mO·cm2 and 100 O·cm2.
The patent further describes a method for manufacturing the transistor, which involves providing the substrate and drift layer with specific doping types and concentrations, depositing the source and drain contacts, and creating the junction implant and recombination region through ion implantation. The method also includes performing high temperature oxidation of the drift layer to increase the carrier lifetime of minority carriers.
Overall, this patented transistor design offers improved performance characteristics, particularly in terms of breakdown voltage and on-state resistance. The inclusion of the body diode and recombination region contributes to these improvements, making it a promising development in the field of transistor technology.
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GlobalData, the leading provider of industry intelligence, provided the underlying data, research, and analysis used to produce this article.
GlobalData Patent Analytics tracks bibliographic data, legal events data, point in time patent ownerships, and backward and forward citations from global patenting offices. Textual analysis and official patent classifications are used to group patents into key thematic areas and link them to specific companies across the world’s largest industries.
