High breakdown voltage and high frequency field-effect transistors on heteroepitaxial diamond film.

为了实现大功率、高频晶体管等高性能金刚石电子器件，人们在氢封端的金刚石表面导电层上制备了场效应晶体管。为了提高场效应晶体管的性能，自对准栅制造工艺可以减小栅长和寄生电阻。采用自对准栅FET工艺，1 μ mCu栅MESFET的漏电流达到110 mS/mm，超过了同等栅尺寸SiC-FET和Si-nMOSFET的漏电流。高性能金刚石MISFET也已经利用相同的工艺实现。利用CaF_2绝缘层作为栅绝缘层，在1.2 μm栅长下，获得了86 mS/mm的最高栅电流密度。MISFET的沟道迁移率高达250 cm^2/Vs，是反型SiC MOSFET的两倍多。首次测量了金刚石MESFETs和MISFET的射频性能。在带宽为70 mS/mm时，2 μm栅MESFET的截止频率为2.2 GHz。而栅长为0.7 μm的金刚石MISFET的截止频率高达11 GHz。该值比2 μm栅MESFFET高5倍。利用栅绝缘层电容与表面沟道电容串联的MIS结构，使源栅电容比金刚石MESFET减小一半。该FET的最高fmax为22 GHz，在2 GHz时获得15 dB的功率增益。

For the realization of high performance diamond electronic devices such as high power and high frequency transistors, FETs have been fabricated on hydrogen-terminated diamond surface conductive layer. In order to improve the performance of FETs, self-aligned gate fabrication processes which can reduce the gate length and parasitic resistances have been developed. Utilizing self-aligned gate FET fabrication process, 1 μm Cu gate MESFET realizes high transconductance of 110 mS/mm. This value exceeds the transconductance of SiC-FETs and Si-nMOSFETs of equal gate size. High performance diamond MISFETs have been also realized utilizing the same process. CaF_2 insulator which does not generate the high interface states density between hydrogen-terminated diamond is utilized as gate insulator.The highest transconductance of 86 mS/mm is obtained in 1.2 μm gate length. The MISFET shows high channel mobility of more than 250 cm^2/Vs. This value is more than twice higher than that of inversion type SiC MOSFETs. The high channel mobility is explained by the screening effect.The RF performances of diamond MESFETs and MISFETs are measured for the first time. The cut-off frequency of 2 μm gate MESFET with transconductance of 70 mS/mm shows 2.2 GHz. On the other hand, much higher cut-off frequency of 11 GHz is realized in diamond MISFET with 0.7 μm gate length. This value is 5 times higher than 2 μm gate MESFETs. Utilizing MIS structure which has gate insulator capacitance in series to surface-channel capacitance, the source to gate capacitance is reduced half as much as that of diamond MESFET. This FET also shows highest fmax of 22 GHz and 15 dB of power gain is obtained at 2 GHz.