The invention provides a preparation method of a
low noise GaN HEMT device. The preparation method comprises the steps that 1) an AlGaN / GaN
heterojunction material with a component gradient back barrier grows; 2) a medium field plate is prepared; 3)
ohmic contact is prepared; 4) an isolation region of the device is formed; 5) a gamma type gate of a TaN radical is formed through a positive
photoresist stripping method; 6) by using a
plasma deposition method, a Si3N4 / SiO2 / Si3N4 multilayer surface
passivation medium is deposited on the surface of a sample; and 7) through a
plasma etching method,
dielectric materials on a source drain and a gate
electrode are removed, so as to form a test window. The preparation method has the advantages that 1) a structure is compatible with power GaN HEMT, which is conductive to
process integration; 2)
voltage resistance of the device is effectively improved, and the degradation of frequency characteristics is prevented; 3) the device's ability to bear
high input power is improved; and 4) the effect of a
passivation process on the device frequency is reduced, and at the same time the gate stability is improved.