Panasonic Corporation has developed a Gallium Nitride (GaN) -based power transistor with a blocking voltage of 600V which "enables stable switching operations." Panasonic began shipping evaluation samples at the end of March. The schedule for full production has not been announced. According to the company, failure-free operations by 600V GaN power transistors are confirmed for the first time. Tentative specifications for production devices is: Threshold voltage of 1.2V; Blocking voltage of 600V; Drain current (continuous) rated for 15A; On-state resistance of 65mÎ©; and Gate charge of 11nC.
When reporting this GaN development, Panasonic noted: Power switching systems require normally-off operations of the transistors for the safe operations. Lowering the cost of the substrate to be employed for the growth of GaN-based films is also required for the GaN transistors to be practically used. Panasonic solved these issues with its novel normally-off Gate Injection Transistors (GITs) on cost-effective Si substrates. Panasonic’ s proprietary technologies for the epitaxial growth of GaN by metal organic chemical vapor deposition (MOCVD) enable the fabrication of GaN transistors over a 6-inch Si substrate. The p-type gate of the GIT greatly helps to reduce the on-state resistance taking advantages of conductivity modulation.
So far, the increase of the on-state resistance after the application of high voltage, so-called current collapse, has been a serious problem for the commercialization of GaN transistors. The increase is the greatest obstacle to achieve the stable operations of the transistors. The origin of the collapse is believed to be trapped electrons under high electric field. Panasonic reduce the number of the traps by its novel processing technologies, in addition to new device structures relieving the electric field. The fabricated GIT on Si enables stable 600V operations free from the current collapse.
The lateral structure of the GIT is advantageous for high-speed switching owing to the lower parasitic capacitance than that in conventional Si-based power transistors with the vertical structures. Here, Ron*Qg (Ron: on-state resistance, Qg: gate charge) is a figure-of-merit for high speed switching. The fabricated GIT exhibits the low Ron*Qg of 715mÎ©nC which is one-thirteenth lower than that by the state-of-the-art Si MOS transistors indicating the superior potential. Panasonic also demonstrated 1MHz operation of resonant LLC dc-dc converters at high efficiency over 96% by using the GITs on Si. This demonstration indicates that the GIT on Si devices can be used for practical systems free from the operation failure.
Applications for 130 domestic and 112 overseas patents have been filed. This work is partially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, under the Strategic Development of Energy Conservation Technology Project.