Research On Fabrication And Characteristics Of Hydrogen-Terminated Polycrystal Diamond MOSFETs

In the field of semiconductor electronic devices,diamond is regarded as the ultimate semiconductor material.Diamond is a semiconductor with a wide bandgap of 5.5 eV,thermal conductivity of 22 W/?cm.K?,breakdown voltage of 20MV/cm,electron mobility of 4500 cm²/?V.s?,hole mobility of 3800 cm²/?V.s?.The Johnson quality factor of diamond is as high as 3720.These characteristics indicate that it is of great significance to study the application of diamond materials in microwave power devices.In recent years,remarkable progress has been made in the research of hydrogen-terminated diamond field effect transistors.In particular,MOSFETs have obvious advantages in device performance and thermal stability.Based on the above background,the research on polycrystalline hydrogen-terminated diamond MOSFET devices is carried out in this paper.The main work and achievements are as follows:1.Aiming at the problems of high leakage current and high voltage resistance of polycrystalline hydrogen-terminated diamond MOSFETs with MoO₃ gate dielectrics,an optimization scheme is proposed.MoO₃/Al₂O₃ bilayer dielectric polycrystalline hydrogen-terminated diamond MOSFET devices were fabricated for the first time.the saturation current of the transistors with 4?m and 2?m gate is 220 mA/mm and 120mA/mm respectively.This has reached the international leading level.The leakage current of the gate of the device has been greatly controlled.The leakage current of the gate is controlled below 10^-9 A in the range of?+5 V?gate voltage.When the gate voltage is-5 V,the device characteristics do not deteriorate significantly.It is shown that MoO₃/Al₂O₃bilayer dielectric devices can effectively control gate leakage while obtaining high saturated output current.2.The band of Al₂O₃ and polycrystalline hydrogen-terminated diamond surfaces were measured.The conclusion is that the valence band and conduction band of Al₂O₃ are located at the 3.06 eV below the valence band of the polycrystalline hydrogen-terminated diamond and 1.96 eV below the conduction band of the polycrystalline hydrogen-terminated diamond,which indicate that Al₂O₃ is suitable for direct contact with polycrystalline hydrogen-terminated diamond surface as gate dielectric,which can effectively control the channel charge density and suppress gate leakage current.Al/Al₂O₃/hydrogen-terminated polycrystalline diamond MOS structures were prepared to study their electrical properties.The I-V characteristics show that the leakage current is at the noise level in the range of+14 V to-8 V,which is below 10^-10 A.The maximum capacitance density of the MOS structure is 0.33?F/cm².There is no dispersion in the different frequency C-V test.Subsequently,the structure of the transistor without interspace between the source and the gate is simulated.The simulation results show that the structure can really increase the characteristics of the device.3.The transistor without interspace between the source and gate are fabricated.The characteristics of the transistor without interspace between the source and gate are introduced.The transistor with 6?m gate and without interspace between the source and gate and the transistor with 6?m and 4?m gate with interspace between the source and gate are measured and analyzed.The maximum saturation drain current density are 150mA/mm,78 mA/mm and 151 mA/mm respectively.The on/off ratios of the three transistors are all in the order of 10^-10,and have reached the international advanced level.The breakdown voltage of the three devices is-14 V,-146 V and-150 V respectively,and the breakdown mechanism of the three devices is analyzed in detail.Finally,30 repeated measures were performed on the transistor.The results showed that the repetitive measure did not cause the transistor degradation,and the stability of the repetitive measuring of the transistor was greatly improved.