Kong Yuechan

Thin-barrier enhancement-mode AlGaN/GaN MIS-HEMT using ALD Al2O3 as gate insulator*

A high-performance enhancement-mode (E-mode) gallium nitride (GaN)-based metal–insulator–semiconductor high electron mobility transistor (MIS-HEMT) that employs a 5-nm-thick aluminum gallium nitride (Al0.3Ga0.7N) as a barrier layer and relies on silicon nitride (SiN) passivation to control the 2DEG density is presented. Unlike the SiN passivation, aluminum oxide (Al2O3) by atomic layer deposition (ALD) on AlGaN surface would not increase the 2DEG density in the heterointerface. ALD Al2O3 was used as gate insulator after the depletion by etching of the SiN in the gate region. The E-mode MIS-HEMT with gate length (LG) of 1 μm showed a maximum drain current density (IDS) of 657 mA/mm, a maximum extrinsic transconductance (gm) of 187 mS/mm and a threshold voltage (Vth) of 1 V. Comparing with the corresponding E-mode HEMT, the device performances had been greatly improved due to the insertion of Al2O3 gate insulator. This provided an excellent way to realize E-mode AlGaN/GaN MIS-HEMTs with both high Vth and IDS.

A Substitution for the High-k Dielectric in an AlGaN/GaN Metal-insulator-Semiconductor Heterostructure

Paraelectric state ferroelectric material is proposed as a novel substitution for the conventional high-k dielectric used in AlGaN/GaN metal-insulator-semiconductor (MIS) field-effect transistors. Its superior potential for improving device transconductance is due to its unique switchable polar nature. By self-consistent calculation involving the switchable polarization of the paraelectric, the 2DEG properties and C—V characteristics are investigated and compared for the novel AlGaN/GaN metal-paraelectric-semiconductor (MPS) structure and an equivalent conventional MIS structure. It is shown that owing to the paraelectric polarization, the gate control of the 2DEG density is remarkably enhanced in the MPS structure and the gate capacitance is significantly improved with a smaller threshold voltage. The self-consistent polarization of the paraelectric in the MPS structure is non-linearly dependent on the saturated polarization, which implies an optimum saturated polarization of 5–10 μC/cm2 for the paraelectric.

220GHz on-wafer measurement based on TRL calibration method

This paper introduced a thru-reflect-line (TRL) calibration standard design for on-wafer measurement. The calibration kits were simulated and fabricated on Indium Phosphide (InP) substrate. The calibration kits covered a range of frequencies from 70 to 220 GHz. On-wafer calibration performed with the microstrip transmission line style contacts was described in this work . The calibration is sufficient to extract reliable device data from measurements. This paper also described a thru de-embedding method . This method show reasonable performance up to 60 GHz. Thru de-embedding method and TRL calibration are compared with the simulated transmission lines up to 220 GHz. The measurement result with TRL calibration method shows good agreement with the simulation result.

AlGaN/GaN HEMTs on 4-Inch Silicon Substrates in the Presence of 2.7-μm-Thick Epilayers with the Maximum Off-State Breakdown Voltage of 500 V

We report on the high breakdown performance of AlGaN/GaN high electron mobility transistors (HEMTs) grown on 4-inch silicon substrates. The HEMT structure including three Al-content step-graded AlGaN transition layers has a total thickness of 2.7 μm. The HEMT with a gate width WG of 300 μm acquires a maximum off-state breakdown voltage (BV) of 550 V and a maximum drain current of 527 mA/mm at a gate voltage of 2 V. It is found that BV is improved with the increase of gate-drain distance LGD until it exceeds 8 μm and then BV is tended to saturation. While the maximum drain current drops continuously with the increase of LGD. The HEMT with a WG of 3 mm and a LGD of 8 μm obtains an off-state BV of 500 V. Its maximum leakage current is just 13 μA when the drain voltage is below 400 V. The device exhibits a maximum output current of 1 A with a maximum transconductance of 242 mS.

High-performance enhancement-mode AlGaN/GaN MOS-HEMTs with fluorinated stack gate dielectrics and thin barrier layer*

We present high-performance enhancement-mode AlGaN/GaN metal—oxide—semiconductor high-electron mobility transistors (MOS-HEMTs) by a fluorinated gate dielectric technique. A nanolaminate of an Al2O3/La x Al1−x O 3/Al2O3 stack (x≈0.33) grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer. Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique, delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm. The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications.

Positive Bias Temperature Instability and Hot Carrier Injection of Back Gate Ultra-thin-body In0.53Ga0.47As-on-Insulator n-Channel Metal-Oxide-Semiconductor Field-Effect Transistor*

Ultra-thin-body (UTB) Ino.53Gao.47As-on-insulator (Ino.53Gao.47As-OI) structures with thicknesses of 8 and 15nm are realized by transferring epitaxially grown Ino.53Gao.47As layers to silicon substrates with 15-nm-thick Al2O3 as a buried oxide by using the direct wafer bonding method. Back gate n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) are fabricated by using these Ino.53Gao.47As-OI structures with excellent electrical characteristics. Positive bias temperature instability (PBTI) and hot carrier injection (HCI) characterizations are performed for the Ino.53Gao.47As-OI nMOSFETs. It is confirmed that the Ino.53Gao.47As-OI nMOSFETs with a thinner body thickness suffer from more severe degradations under both PBTI and HCI stresses. Moreover, the different evolutions of the threshold voltage and the saturation current of the UTB Ino.53Gao.47As-OI nMOSFETs may be due to the slow border traps.

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.

Influence of Polarization Effects on the Energy Band of AlGaN/GaN/AlGaN Heterostructures

The unintentionally doped samples of Al0.22Ga0.78N/GaN/Al0.22Ga0.78N/GaN multi-heterostructures have been designed and fabricated. The polarization induced charge and free-carrier charge distributions have been demonstrated and the energy band profile has also been calculated. The results indicate the existence of two-dimensional electron gas (2DEG) and hole well at the heterointerfaces. By means of variable temperature Hall measurements, the carrier mobility and the sheet carrier density were measured from 300 to 77 K. The significant increment of carrier mobility at low temperature also verified the existence of the 2DEG.