GaN HEMT WITH AlGaN BACK-BARRIER FOR HIGH POWER MILLIMETRE WAVE APPLICATIONS

William, STATIC AND DYNAMIC CHARACTERISTICS OF Lg 50 nm InAlN/AlN/GaN HEMT WITH AlGaN BACK-BARRIER FOR HIGH POWER MILLIMETRE WAVE APPLICATIONS, Journal of Science: Advanced Materials and[r]

STATIC AND DYNAMIC CHARACTERISTICS OF Lg 50 nm InAlN/AlN/GaN

HEMT WITH AlGaN BACK-BARRIER FOR HIGH POWER MILLIMETRE WAVE

APPLICATIONS

P Murugapandiyan, Assistant Professor, S Ravimaran, Professor, J William,

Professor

DOI: 10.1016/j.jsamd.2017.08.004

To appear in: Journal of Science: Advanced Materials and Devices

Received Date: 21 January 2017

Revised Date: 21 July 2017

Accepted Date: 7 August 2017

Please cite this article as: P Murugapandiyan, S Ravimaran, J William, STATIC AND DYNAMIC CHARACTERISTICS OF Lg 50 nm InAlN/AlN/GaN HEMT WITH AlGaN BACK-BARRIER FOR HIGH

POWER MILLIMETRE WAVE APPLICATIONS, Journal of Science: Advanced Materials and Devices

(2017), doi: 10.1016/j.jsamd.2017.08.004.

This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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STATIC AND DYNAMIC CHARACTERISTICS OF Lg 50nm InAlN/AlN/GaN HEMT WITH AlGaN BACK-BARRIER FOR HIGH POWER MILLIMETRE WAVE APPLICATIONS

P.Murugapandiyan 1 , S.Ravimaran 2 , J.William 3

1 Assistant Professor, Department of Electronics and Communication Engineering, Agnel Institute of

Technology and Design, Goa-India

2 Professor, Department of Electrical and Computer Science, M.A.M College of Engineering, Trichy,Tamilnadu,

3 Professor, Department of Electronics and Communication Engineering, M.A.M College of Engineering and

Technology, Trichy,Tamilnadu, India

Email: murugavlsi@gmail.com

Authors

P.Murugapandiyan has received his B.E in Electronics and Communication Engineering

from Anna University , Chennai, Tamil Nadu, India in 2008 and he received Master of Engineering in VLSI Design from Anna University, Chennai, Tamil Nadu, India in the year

2013 He is pursuing Ph.D at Anna University, Chennai, Tamilnadu- India Now he is working as Assistant Professor in the Department of Electronics and Communication Engineering, Agnel Institute of Technology and Design, Goa-India His research focuses on modelling and simulation of III–N compound semiconductor materials and devices for future high speed with high power MMIC applications

Dr.S.Ravimaran , Principal and Professor in Computer Science and Electrical Engineering

department of the M.A.M College of Engineering, Tamil Nadu,India and he has received his B.E in computer science and engineering from National Institute of Technology, Tiruchirapalli, India in 1997 and his M.E Computer science and engineering from Anna

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University Chennai, India in 2013 His research interests are High speed wireless Communication Networks and wide band attenna design for MMIC RF applications

Dr.J.William, Principal and Professor in Electronics and Communication Engineering

department of the M.A.M College of Engineering and Technology, Tamil Nadu-India and he

has received Doctor of Philosophy in the area of ULTRA WIDEBAND ANTENNA, Pondicherry Central University, Pudhucherry, India, in the year 2011 and Master of Technology with the specialization of Communication Systems at NIT, Trichy in the year

2006 His research interests are GaN based High power amplifier and oscillator design for milli meter wave high power applications

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InAlN/AlN/GaN HEMT WITH AlGaN BACK-BARRIER FOR HIGH POWER MILLIMETRE WAVE APPLICATIONS

Abstract

In this paper, a novel 50 nm recessed T-gate AlN spacer based InAlN/GaN HEMT with AlGaN back-barrier is designed The static and dynamic characteristics of the proposed device structure are investigated using Synopsys TCAD tool The other device features are

device to suppress the parasitic resistances and capacitances of the transistor for enhancing the microwave characteristics The proposed InAlN/GaN HEMT exhibits the

superior static and dynamic characteristics of InAlN/GaN HEMT obtained, undoubtedly places the device at the forefront for high power millimetre wave applications

Keywords

HEMT, 2DEG, static and dynamic characteristics, cut-off frequency, back-barrier

1.Introduction

Recently the lattice matched InAlN/GaN heterojunction high electron mobility transistors (HEMTS) are of great interest for high power switching and RF applications because of their high breakdown voltage, high current density and thermal stability The limitations of AlGaN/GaN HEMT have been reached now in particular for the bottom part of the mm-wave spectrum (30-300 GHz) Furthermore the unavoidable strain caused by the lattice mismatch between GaN and AlGaN limits the Al contents of the barrier to about 30% and therefore the

A/mm The presence of strain has been identified as a source of failure for these devices (5, 6)

Lattice matched InAlN/GaN HEMTs presents several advantages with respect to AlGaN/GaN They allow for a more efficient downscaling of the transistor dimensions,

InAlN/GaN HEMT have been shown to produce the current density of 2 A/mm (9) Therefore InAlN/GaN based HEMTs are ideal candidates for high power RF applications particularly in the millimeter range frequencies Besides the remarkable potential for high power and high frequency applications, InalN/GaN HEMT has also demonstrated for good thermal stability at 1000ºC (11) However, despite the great potentials of the InAlN/GaN

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HEMTs, are suffering from leakage currents and consequently low breakdown voltages reported (12), as well as strong short channel effects (13) The ohmic contacts were characterized to reduce the contact resistance of ~0.3 Ω.mm (13).Devices for high temperature operation on the other hand from high buffer leakage which strongly degrades the operating temperature of HEMT InAlN/GaN HEMTs Provide a better carrier confinement in the 2DEG than conventional AlGaN/GaN based HEMT due to larger spontaneous polarization between the barrier and channel (6) To reduce the alloy disorder scattering at the InalN/GaN interface, a very thin AlN spacer layer is placed between them which improves the 2DEG density

In this work we have proposed a novel 50 nm recessed T-gate InAlN/GaN HEMT with

gap (6.02 eV) AlN spacer layer along with AlGaN back-barrier provides the effective confinement of electrons in the 2DEG region Moreover, the buffer leakage current is mitigated by the back-barrier and the gate leakage current is majorly suppressed by AlN spacer layer The symmetric gate position and back-barrier are helped the device to achieve higher breakdown voltage, which is essential key factor for high power applications

2 InAlN/GaN HEMT device structure and Band gap Diagram:

The vertical cross section of InAlN/AlN/GaN/AlGaN HEMT device structure is depicted in Fig.1 The device consists of 3 inch SiC substrate to achieve good thermal stability, 1450 nm

Fe doped GaN buffer layer which isolate the channel from the substrate defects, 3.5 nm

its effective conduction band notch at the interface with GaN channel and also it contributed

spacer layer is placed between the barrier and channel which improves the electron mobility

in the 2DEG by reducing the interface roughness and alloy disorder scattering at the interface

of InAlN/GaN The induced spontaneous and piezoelectric polarization electric field provides

higher band gap of the barrier limits the gate leakage current and reduces the short channel effects in the device The source and drain regions are formed by heavily doped GaN (50 nm)

drain ohmic contacts were designed by using Ti/Pt/Au metal stack and T-shaped recessed gate (6nm recess depth) is formed with the head size of 450 nm, stem height of 140 nm with

50 nm footprint is designed, which liftoff wide cross sectional gate area with smaller gate length and Schottky contact is formed by Ni/Pt/Au metal stack The reduction in the gate to drain space can causes the high electric field in the gate-source region which results in high

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distance are kept at 30 nm and 80 nm respectively to maintain a low electrostatic field in the gate-drain space channel region while maintaining enhanced breakdown voltage In order to reduce the parasitic capacitances of the device, finally the device surface is fully passivated

thickness of passivation layer is needed, which will increases the gate capacitance

layer which assists to unfasten the dispersion effects and it provides a root to good transport

property in the 2DEG

Figure.1 Vertical Cross-sectional view of InAlN/AlN/GaN/AlGaN heterostructure

Figure.2 (a) Polarization charge distribution (b) Energy band diagram of HEMT

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The Polarization charge distribution and conduction band offset diagram of InAlN/AlN/GaN/InGaN is depicted in Fig.2 (a) and (b) respectively The InAlN/GaN

InAlN/GaN The high 2DEG density is achieved by the large spontaneous and piezoelectric polarization field inside the InAlN layer Due to induced piezoelectric polarization between AlGaN and GaN there will be a sharp raised potential barrier is formed at the back of 2DEG channel Such a sharp notch helps to confine the electron in better manner in the channel region and also it mitigates the buffer leakage current, which also contributed for improving the breakdown voltage of the transistor A very thin 1 nm wide band gap (6.01 eV) AlN spacer is placed between barrier and channel to offer large effective conduction band offset and also it helps to reduce the gate leakage current

3 Result and discussion

In this article, we have proposed and investigated the static and dynamic characteristics of a novel 50 nm x 20 µm T-gate InAlN/GaN HEMT with AlGaN back-barrier Fig.3 depicts the

Fig.4 shows the V–I characteristics of Lg = 50 nm and W = 20 µm InAlN/AlN/GaN HEMT

because of the enhanced mobility with greater sheet charge carrier density in 2DEG channel The lattice-matched InAlN/GaN with 1 nm SiN spacer provides effective conduction band offset and it reduces strain induced surface defects at the interface Moreover, the AlGaN notch helps to provide better confinement of charge carriers in the channel and also it

source of power dissipation when the transistor working in linear region, the extracted very

applications A 40 V off-state breakdown voltage is obtained from the breakdown characteristics of the proposed HEMT which is depicted in Fig.5

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Fig.6.shows the transconductance variation with the gate bias voltage The maximum

associated drain voltage is 2 V The extracted threshold voltage of the device from the transfer characteristics shown in Fig.7 is -1.5 V

The short channel effects (SCEs) are the major problems in nanometer regime gate length

gate to channel From the log-scale plot, a very small 63 mV/V drain induced barrier

subthreshold characteristics shown in Fig.8 Moreover, the improved Ion/Ioff ratio of ~105 is achieved, which is important factor for high speed switching applications The gate leakage

of 1 nm AlN spacer layer effectively suppressed the gate leakage current for such a smaller

Figure.3 Sheet charge density dependency on barrier layer thickness

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HEMT

HEMT

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InAlN/GaN HEMT

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Figure.11 cut-off frequency variation of InAlN/GaN HEMT for different gate length

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Current gain Cut-off frequency:

          /     

Power gain cut-off frequency:

   "   

(2)

() + & + , -.

( ) and drain resistance $/ = &'

() +

& + , 0

( ) $1 and $%2 are the contact resistance and channel sheet resistance respectively

device model

frequencies of 50 nm gate length GaN-based HEMT with a high current density of 2.1 A/mm

resistances (Rd and Rs), gate resistance (Rg) and parasitic capacitances (Cgs and Cgd) of the device mainly because of heavily doped (n++ GaN) source / drain regions has direct contacts with the channel, combined with drain /source access region, passivated device surface, and a

enhancing the mobility by providing large gate area Moreover, the minimum short channel

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Table.1 Recent Research Progress in GaN-based HEMTs for High Power RF applications

(GHz)

(V)

SCEs

SS 80 mV/dec

5 Conclusion

The static and dynamic characteristics of a novel 50 nm recessed T-gate InAlN/GaN HEMT with AlGaN back-barrier has been studied by using Synopsys TCAD tool The

passivated device surface, which are helped to reduce the contact resistances and parasitic

achieved by offering effective conduction band offset by using InAlN barrier material associated with back-barrier by enhancing the sheet charge carrier density in 2DEG region

associated with the back-barrier structure The short channel effects (SCEs) are greatly suppressed by providing good aspect ratio with the help of recessed gate This excellent DC and microwave characteristics of the proposed HEMT device makes them the most suitable candidate for future high power millimetre wave RF applications

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The authors acknowledge the Nanoelectron Device Laboratory of Electronics and Communication Engineering Department at M.A.M College of Engineering, Trichy-India for providing all facility to carry out this research work

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