Towhidur Razzak

The Ohio State University

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Siddharth Rajan

The Ohio State University

Hao Xue

Tohoku University

Wu Lu

The Ohio State University

Shahadat H. Sohel

National Renewable Energy Laboratory

Asif Khan

University of South Carolina

Sanyam Bajaj

The Ohio State University

Zhanbo Xia

The Ohio State University

Mohammad Wahidur Rahman

The Ohio State University

Kamal Hussain

University of South Carolina

Hareesh Chandrasekar

Indian Institute of Science Bangalore

Cooperative Institutions

The Ohio State University

University of California, Santa Barbara

University of South Carolina

Qorvo (United States)

University of Delaware

Vanderbilt University

Sandia National Laboratories

IAP Research (United States)

University of Utah

Indian Institute of Technology Bombay

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Integration of high permittivity BaTiO3 with AlGaN/GaN for near-theoretical breakdown field kV-class transistors

Applied Physics Letters (2021)

Mohammad Wahidur Rahman Nidhin Kurian Kalarickal Hyunsoo Lee Towhidur Razzak Siddharth Rajan

In this Letter, we discuss AlGaN/GaN HEMTs integrated with high permittivity BaTiO3 dielectric to enable enhanced breakdown characteristics. We show that using high permittivity BaTiO3 dielectric layers in the gate and drain access regions prevents premature gate breakdown, leading to average breakdown fields exceeding 3 MV/cm at a gate-to-drain spacing of 4 μm. The higher breakdown fields enable a high power figure of merit above 2.4 GW/cm2 in devices with a gate-to-drain spacing of 6 μm. This work demonstrates that electrostatic engineering using high-permittivity dielectrics can enable AlGaN/GaN HEMTs in approaching the material breakdown field limits.

Figure of Merit

Wide-bandgap semiconductor

Dielectric strength

10.1063/5.0070665

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Citations (16)

RF Performance of 130 nm Al_0.75Ga_0.25N/Al_0.6Ga_0.4N HFETs with MBE-Regrown Contacts

Hao Xue Choong Hee Lee Kamal Hussian Towhidur Razzak Abdullah Mamun

AlGaN channel transistors are promising candidates for high power RF transistors due to their superior material properties. The larger breakdown field and similar saturation velocity compared to GaN make AlGaN channel transistors potentially capable of delivering higher power density at high frequencies. So far the highest reported fT is 28 GHz on Al _0.85 Ga _0.15 N/Al _0.70 Ga _0.30 N transistors with RF power density of 0.3 W/mm at 3 GHz [1]. The major obstacle to achieve high RF performance is the challenge to form good ohmic contacts to Al-rich AlGaN. Here, we show significantly better small and large signal RF performance than what have been reported on high Al-composition AlGaN transistors with regrown side contacts.

Ohmic contact

10.1109/drc46940.2019.9046394

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Polarization Engineering of AlGaN/GaN HEMT With Graded InGaN Sub-Channel for High-Linearity X-Band Applications

IEEE Electron Device Letters (2019)

Shahadat H. Sohel Andy Xie Edward Beam Hao Xue Towhidur Razzak

We report on the power and linearity performance of metal-organic chemical vapor deposition grown polarization-engineered novel structure that combines the AlGaN/GaN high-electron-mobility transistor with a graded InGaN sub-channel layer. The fabricated transistors with composite two-dimensional(2D) and three-dimensional(3D) electron channels showed nearly flat transconductance and power gain profiles. The maximum f _T and f _max values of 18 GHz and 38 GHz were measured for 0.7-μm gate-length transistors. Load-pull measurement at 10 GHz revealed a maximum output power of 2.2 W/mm. Two-tone measurement at 10 GHz showed an excellent OIP3 of 38 dBm for 150-μm device width and a corresponding linearity figure of merit OIP3/P _DC of 9.7 dB. These results suggest that InGaN-based composite 2D-3D channel transistors could be useful for high-frequency applications requiring high linearity.

Transconductance

Linearity

Figure of Merit

10.1109/led.2019.2899100

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Citations (35)

Ultra-Wide Bandgap Al_xGa_1-xN Channel Transistors

International Journal of High Speed Electronics and Systems (2019)

Towhidur Razzak Siddharth Rajan Andrew Armstrong

High Al-composition Al x Ga 1-x N, an emerging class of materials, is gaining significant traction due to its high critical breakdown electric field exceeding that of GaN and high electron saturation velocity that is comparable to GaN. High Al-composition Al x Ga 1-x N holds promise for applications such as highly scaled next generation RF devices and power devices. However, significant strides remain to be made before Al x Ga 1-x N can take a share of the limelight. Encouraging progress has been made in recent years, including multiple reports of RF operation of Al x Ga 1-x N channel transistors with reported unity current gain cutoff frequency as high as 40 GHz, high current density devices with the maximum reported current density exceeding 600 mA/mm and reports of breakdown fields in lateral transistors that are almost 3× the reported breakdown field for GaN channel devices of similar dimensions. This paper focuses on the lateral devices demonstrated thus far and discusses breakthrough performance results achieved for Al x Ga 1-x N channel transistors together with the key challenges that are yet to be properly addressed. The paper starts with a discussion of contact formation to Al x Ga 1-x N films – the key difficulty of fabricating Al x Ga 1-x N transistors. This is followed by a discussion of the types of devices that are typically used. This is followed up with a discussion of the approach required to make high quality devices with Al x Ga 1-x N as a template together with some recent result highlights.

Saturation velocity

10.1142/s0129156419400093

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Citations (4)

Improved DC-RF dispersion with epitaxial passivation for high linearity graded AlGaN channel field effect transistors

Applied Physics Express (2020)

Shahadat H. Sohel Andy Xie Edward Beam Hao Xue Towhidur Razzak

We demonstrate DC-RF dispersion-free graded AlGaN channel transistor with an epitaxial passivation. The device used for this experiment was an AlGaN channel polarization-graded field effect transistor (PolFET) with Al-composition grading from 0% to 30%. We were able to reduce the dispersion to almost zero current collapse and zero knee-walkout for pulsed I–V up to 30 V drain quiescent bias condition with epitaxial passivation, compared to 8 V knee-walkout and 25% current collapse for PolFETs with traditional PECVD SiNx for the same measure conditions. We also report large signal power density and two-tone linearity for these devices up to X-band frequencies.

Passivation

Linearity

10.35848/1882-0786/ab7480

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All MOCVD grown 250 nm gate length Al_0.70Ga_0.30N MESFETs

Hao Xue Towhidur Razzak Seongmo Hwang Antwon Coleman Sanyam Bajaj

High Al-composition AlGaN materials, by virtue of their ultra-wide band gap, are promising candidates for realizing high power density mm-wave transistors. However, low electron affinity in these materials make it very difficult to make ohmic contacts for Al-composition above 65%. On the other hand, to achieve high cutoff frequency, it is critical to scale the transistors. In this work, we report the first ever DC and small-signal RF performance of a scaled MOCVD-grown UWBG A _10.70 Ga _0.30 N MESFET with L _G = 250 nm.

MESFET

Ohmic contact

10.1109/drc.2018.8442167

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Citations (2)

Al_0.7Ga_0.3N MESFET With All-Refractory Metal Process for High Temperature Operation

IEEE Transactions on Electron Devices (2021)

Alex M. Potts Sanyam Bajaj David R. Daughton Andrew A. Allerman Andrew Armstrong

Ultrawide bandgap Al _0.7 Ga _0.3 N MESFETs with refractory Tungsten Schottky and Ohmic contacts are studied in 300-675 K environments. Variable-temperature dc electrical transport reveals large ON-state drain current densities for an AlGaN device: 209 mA/mm at 300 K and 156 mA/mm at 675 K in the ON-state (25% reduction). Drain and gate currents are only weakly temperature-dependent, suggesting potential for engineering temperature invariant operation. The ON-/ OFF-ratio is limited by OFF-state leakage through the gate, which is attributed to damage from sputter deposition. Future work using refractory metals with larger work functions that are deposited by electron beam deposition is proposed.

MESFET

Ohmic contact

Refractory metals

10.1109/ted.2021.3095138

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Al_0.65Ga_0.35N/Al_0.4Ga_0.6N Micro-Channel Heterojunction Field Effect Transistors With Current Density Over 900 mA/mm

IEEE Electron Device Letters (2020)

Hao Xue Kamal Hussain Towhidur Razzak Mikhail Gaevski Shahadat H. Sohel

We report on the demonstration of high current density in Al _0.65 Ga _0.35 N/Al _0.4 Ga _0.6 N heterojunction field effect transistors with micro-channels enabled by enhanced contact injection. Devices with a gate length of 100 nm exhibited a maximum current density of 910 mA/mm and a maximum transconductance of 140 mS/mm. A current gain cut off frequency of 20 GHz and maximum oscillation frequency of 36 GHz were obtained. Large-signal load-pull characterization of the transistors showed output power density of 2.7 W/mm at 10 GHz. The current density and output power density represent the state-of-art performance for high Al-composition AlGaN channel transistors.

Transconductance

10.1109/led.2020.2977997

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Citations (24)

Preface

International Journal of High Speed Electronics and Systems (2019)

Uttam Singisetti Towhidur Razzak Yuewei Zhang

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Zhàng

10.1142/s0129156419020014

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RF operation in graded Al _x Ga _{1− x} N ( x = 0.65 to 0.82) channel transistors

Electronics Letters (2018)

Towhidur Razzak Seong Mo Hwang Antwon Coleman Sahil Bajaj Hao Xue

The first report is presented on the RF operation of AlGaN channel transistor with Al‐composition above 80%. The reported device is a polarisation‐graded field effect transistor (PolFET) featuring an ultra‐wide bandgap (UWBG) AlGaN channel with Al‐composition grading from 65 to 82%. Transistors with a gate length of 0.8 μm were fabricated, with a current density of 265 mA/mm, the highest observed for AlGaN channel transistor with Al‐composition above 80%, and f T / f MAX of 5.4/14.2 GHz. This demonstration of RF operation of polarisation‐graded transistor provides a direction for achieving ultra‐wide bandgap AlGaN based devices for high performance RF and power switching applications.

10.1049/el.2018.6897

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Citations (16)