Diamond Metal Insulator Semiconductor Field Effect Transistor Research Articles

Diamond inverter consisted of high mobility and low on-resistance enhancement-mode C[sbnd]H diamond MISFET

Hydrogenated diamond (CH diamond) inverters have been fabricated by normally-off Al/BaF2/C-H diamond metal-insulator-semiconductor field effect transistors (MISFETs) and load resistors. Electron beam evaporation was used to deposit BaF2 film on the diamond surface at room temperature to reduce thermal degradation effect on the CH bond and adsorbates during the deposition. The resulting 4-μm normally-off MISFET achieves the maximum saturation drain current, on-resistance, maximum transconductance and switching ratio of −113.4 mA/mm, 37.1 Ω·mm, 35.4 mS/mm and 108, respectively. Effective hole mobility of more than 200 cm2/V·s is achieved in a large gate voltage range (−0.35 V ≤ VGS -VTH ≤ −4.35 V). Correspondingly, based on the high-performance diamond MISFET, the diamond inverters exhibit good voltage transfer characteristics and dynamic switching characteristics at the frequency of 50 kHz.

Normally-off polycrystalline C[sbnd]H diamond MISFETs with MgF2 gate insulator and passivation

We report a normally-off CH diamond metal-insulator-semiconductor field effect transistor (MISFET) using a 15-nm-thick thermally evaporated MgF2 film as both the gate dielectric and the passivation layer. The normally-off channel is directly formed based on the Al/MgF2/C-H diamond MIS gate structure. The 4-μm device delivers a record high transconductance (gm) of 26.2 mS/mm among normally-off CH diamond FETs, and a threshold voltage of −0.60 V, a maximum μeff of 138.9 cm2/V·s, a maximum drain current (IDmax) of −49.7 mA/mm and an on-resistance (Ron) of 84.4 Ω·mm at the gate voltage of −5 V. The low Ron and high gm and large IDmax arise from the good conductivity at the MgF2/C-H diamond interface, and the normally-off operation could be attributed to the depletion effect of the gate on the channel with its 2DHG conductivity just slightly degraded after MgF2 deposition.

Low on-resistance diamond field effect transistor with high-k ZrO2 as dielectric.

Although several high-k insulators have been deposited on the diamond for metal-insulator-semiconductor field effect transistors (MISFETs) fabrication, the k values and current output are still not fully satisfactory. Here, we present a high-k ZrO2 layer on the diamond for the MISFETs. The k value for ZrO2 is determined by capacitance-voltage characteristic to be 15.4. The leakage current density is smaller than 4.8 × 10−5 A·cm−2 for the gate voltage ranging from −4.0 to 2.0 V. The low on-resistance MISFET is obtained by eliminating source/drain-channel interspaces, which shows a large current output and a high extrinsic transconductance. The high-performance diamond MISFET fabrication will push forward the development of power devices.

Research on the diamond MISFET

Based on the hydrogen-terminated surface channel diamond material, a 1 μm gate length diamond metal—insulator—semiconductor field-effect transistor (MISFET) was fabricated. The gate dielectric A12O3 was formed by naturally oxidated thin Al metal layer, and a less than 2 pA gate leakage current was obtained at gate bias between −4 V and 4 V. The DC characteristic of the diamond MISFET showed a drain-current density of 80 mA/mm at drain voltage of −5 V, and a maximum transconductance of 22 mS/mm at gate—source voltage of −3 V. With the small signal measurement, a current gain cutoff frequency of 2.1 GHz was also obtained.

Fabrication of T-Shaped Gate Diamond Metal–Insulator–Semiconductor Field-Effect Transistors

Diamond metal–insulator–semiconductor field effect transistors (MISFETs) with gates of 0.2–0.9 µm length and T-shape were realized by trilayer resist electron-beam lithography. FETs show a cut-off frequency ( fT) of 11 GHz and maximum oscillation frequency ( fmax) of 22 GHz. The fmax/ fT ratio of this FET was more than double that of FETs with a conventional gate structure and the same gate length. The fT of 11 GHz was half the maximum for diamond FETs due to parasitic capacitance at the gate–drain and gate–source electrodes. The T-shaped gate structure and the source-to-drain spacing must be optimized to reduce parasitic capacitance between each electrode.

Characterization of diamond metal-insulator-semiconductor field-effect transistors with aluminum oxide gate insulator

Metal-insulator-semiconductor field-effect transistors (MISFETs) with aluminum oxide as a gate insulator have been fabricated on a hydrogen-terminated diamond surface using its surface conductive layer. The aluminum oxide gate insulator was deposited on the diamond surface by the pulsed laser deposition method. The on-off ratio measured by dc was greater than five orders of magnitude, one of the best results reported for diamond FETs. The gate leak current of aluminum oxide MISFETs is three orders of magnitude less than that of conventional CaF2 MISFETs. These characteristics indicate that aluminum oxide gate insulators are suitable for high reliability power device applications of diamond MISFETs.

Fabrication of diamond MISFET with micron-sized gate length on boron-doped (111) surface

A hydrogenated surface conductive layer of B-doped diamond on (111) was employed to fabricate a metal insulator semiconductor field effect transistor (MISFET) using a CaF 2 and Cu stacked gate. The carrier mobility and concentration of the hydrogenated surface on (111) before FET processing were 35 cm 2/V s and 10 13/cm 2, respectively, when bulk carrier concentration and film thickness of the B-doped underlaying diamond was 3 × 10 15/cm 3 and 1.5 μm, respectively. The DC characteristics of the gate with 1.1 μm length and 50 μm width showed that the maximum measured drain current was 240 mA/mm at − 3.0 V gate voltage, and the maximum transconductance ( g m) was 70 mS/mm. The cut-off frequency of 4 GHz was obtained, which is one of the best values for the RF characteristics of a diamond homoepitaxial (111) MISFET.

Device operation of p-i-p type diamond metal–insulator–semiconductor field effect transistors with sub-micrometer channel

Sub-micrometer p-i-p type diamond metal–insulator–semiconductor field effect transistors (FETs), which are composed by p + layers by B ion implantation and intrinsic channels deposited by a selective epitaxy, are fabricated. The current flow in the FET with a sub-micrometer channel are investigated by repeating measurements under a same bias sweep, and the current drift and the degradation of the device characteristics between the repeated measurements are observed. Distribution of the current density in the fabricated FET is analyzed by using a device simulator. The conduction mechanism and the carrier paths in the devices are discussed.

Electrical Properties of Diamond MISFETs with Submicron-Sized Gate on Boron-Doped (111) Surface

ABSTRACTAn H-terminated-surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal insulator semiconductor field effect transistor (MISFET) using CaF2, SiO2 or Al2O3 gate insulators and a Cu-metal stacked gate. For a CaF2 gate, the maximum measured drain current (Idmax) was 240 mA/mm and the maximum transconductance (gm) was 70 mS/mm, and the cut-off frequency of 4 GHz was obtained. For a SiO2 gate, Idmax and gm were 75 mA/mm and 24 mS/mm, respectively, and for an Al2O3 gate, these characteristics were 86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported DC and RF characteristics for a diamond homoepitaxial (111) MISFET.

Over 20-GHz Cutoff Frequency Submicrometer-Gate Diamond MISFETs

Submicrometer-gate (0.2-0.5-/spl mu/m) diamond metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated on an H-terminated diamond surface. The maximum transconductance in dc mode reaches 165 mS/mm, while the average transconductance is 70 mS/mm in submicrometer-gate diamond MISFETs. The highest cutoff frequency of 23 GHz and the maximum frequency of oscillation of 25 GHz are realized in the 0.2-/spl mu/m-gate diamond MISFET. From the intrinsic transconductances or the cutoff frequencies, the saturation velocities are estimated to be 4/spl times/10/sup 6/ cm/s in the submicrometer-gate FETs. They are reduced by gate-drain capacitance and source resistance.

High performance diamond MISFETs using CaF 2 gate insulator

A cut-off frequency of 15 GHz and a maximum frequency of oscillation of 20 GHz are realized in a 0.4-μm gate diamond metal–insulator–semiconductor field-effect transistor (MISFET). The cut-off frequency is the highest value for diamond FETs ever reported. The RF characteristics of the MISFETs are higher than those of metal–semiconductor FETs at the same gate lengths. The CaF 2 gate insulator improves the carrier mobility according to the Hall measurement system. The mobility increases in the surface conductive layer result in high RF performance. The source–gate passivation of CaF 2 results in the high DC transconductance because of the reduction of series resistances. A cut-off frequency of more than 30 GHz is expected with the gate minimization and the CaF 2 passivation of source–gate and gate–drain spacings.

DC and RF characteristics of 0.7-μm-gate-length diamond metal–insulator–semiconductor field effect transistor

A 0.7-μm-gate-length metal–insulator–semiconductor field effect transistor (MISFET) was fabricated on a hydrogen-terminated diamond surface conductive layer. The maximum transconductance of 100 mS/mm was obtained by DC measurement. The cut-off frequency of 11 GHz and the maximum frequency of oscillation of 18 GHz were achieved for the fabricated MISFET biased at VGS=0 V and VDS=−12 V. These are the highest values for diamond MISFETs ever reported. In the MISFET, high-frequency small-signal equivalent circuit analysis is carried out at VGS=0 V and VDS=−3, −5, −8, −10 and −12 V. The analysis indicates that the reduction of parasitic resistance between the source and gate is necessary for realizing higher output power.

RF performance of diamond MISFETs

A cutoff frequency (f/sub T/) of 11 GHz is realized in the hydrogen-terminated surface channel diamond metal-insulator-semiconductor field-effect transistor (MISFET) with 0.7 /spl mu/m gate length. This value is five times higher than that of 2 /spl mu/m gate metal-semiconductor (MES) FETs and the maximum value in diamond FETs at present. Utilizing CaF/sub 2/ as an insulator in the MIS structure, the gate-source capacitance is reduced to half that of the diamond MESFET because of the gate insulator capacitance being in series to the surface-channel capacitance. This FET also exhibits the highest f/sub max/ of 18 GHz and 15 dB of power gain at 2 GHz. The high-frequency equivalent circuits of diamond MISFET are deduced from the S-parameters obtained from RF measurement.

Fabrication of 0.1 µm channel diamond Metal-Insulator-Semiconductor Field-Effect Transistor

ABSTRACTAnalysis of diamond short channel effect is carried out for the first time. 70 nm channel diamond metal-insulator semiconductor field-effect transistor is realized by utilizing new FET fabrication process on the hydrogen-terminated surface conductive layer. This FET is the shortest gate length in diamond FETs. FETs with thick gate insulator of 35 nm show significant threshold voltage shift and degradation of subthreshold slope S by the gate refining. This phenomenon occurs due to the penetration of drain field into channel. However, the degradation of subthreshold performance and threshold voltage shift are hardly observed in 0.17 µm FET with thin gate insulator 15 nm in thickness.