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

为了实现高性能的金刚石电子器件，如大功率、高频晶体管等，人们在氢端金刚石表面的导电层上制作了FET。为了提高场效应管的性能，人们开发了能够减小栅长和寄生电阻的自对准栅极制作工艺。采用自对准栅场效应晶体管制作工艺，1μm铜栅MESFET实现了110ms/mm的高跨导。这一数值超过了栅极尺寸相同的SiC型和Si型nMOSFET的跨导。利用相同的工艺也实现了高性能的金刚石MISFET。采用CaF_2绝缘体作为栅绝缘体，在1.2μm栅长时，获得了最大跨导为86ms/mm，该绝缘体不会在端氢金刚石之间产生高的界面态密度。MISFET的沟道迁移率超过250 cm^2/V。这一数值是反型碳化硅MOSFET的两倍多。首次测量了钻石MESFET和MISFET的射频性能。跨导为70ms/mm的2μm栅MESFET的截止频率为2.2 GHz。另一方面，栅长为0.7μm的金刚石MISFET具有更高的截止频率(11 GHz)。该值是2μm栅MESFET的5倍。利用栅绝缘体电容串联到表面沟道电容的MIS结构，源极到栅极的电容比钻石MESFET减小一半。该场效应管的最大FMAX为22 GHz，在2 GHz下获得了15分贝的功率增益。

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.