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，在端氢金刚石表面导电层上制备了场效应管。为了提高fet的性能，研究了自对准栅极的制备工艺，以减小栅极长度和寄生电阻。采用自对准栅极FET制造工艺，1 μm Cu栅极MESFET实现了110 mS/mm的高跨导。这个值超过了相同栅极尺寸的sic - fet和si - nmosfet的跨导性。利用相同的工艺也实现了高性能的金刚石misfet。采用端氢金刚石之间不产生高界面态密度的CaF_2绝缘子作为栅极绝缘子。当栅极长度为1.2 μm时，跨导率最高，为86 mS/mm。MISFET显示出超过250 cm^2/Vs的高通道迁移率。该值比反转型SiC mosfet高两倍以上。高通道迁移率可以用筛分效应来解释。本文首次测量了金刚石mesfet和misfet的射频性能。跨导70 mS/mm的2 μm栅极MESFET截止频率为2.2 GHz。另一方面，栅极长度为0.7 μm的金刚石MISFET可以实现更高的截止频率，达到11 GHz。该值比2 μm栅极mesfet高5倍。利用栅极绝缘子电容与表面沟道电容串联的MIS结构，源极电容比金刚石MESFET减小了一半。该FET也显示出22 GHz的最高fmax，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.