Design and analysis of 10 nm t gate enhancement mode mos hemt for high power microwave applications

Journal of Science: Advanced Materials and Devices (2019) 180e187 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Design and analysis of 10 nm T-gate enhancement-mode MOS-HEMT for high power microwave applications Touati Zine-eddine a, *, Hamaizia Zahra a, Messai Zitouni b, c a Laboratory of Semiconducting and Metallic Materials, University of Mohamed Khider Biskra, Algeria Electronics Department, Faculty of Sciences and Technology, University of BBA, Algeria c Laboratory of Optoelectronics and Components, UFAS 19000, Algeria b a r t i c l e i n f o a b s t r a c t Article history: Received 17 December 2018 Received in revised form 30 December 2018 Accepted January 2019 Available online January 2019 In this work, we propose a novel enhancement-mode GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with a 10 nm T-gate length and a high-k TiO2 gate dielectric The DC and RF characteristics of the proposed GaN MOS-HEMT structure are analyzed by using a TCAD Software The device features are heavily doped (nỵỵ GaN) source/drain regions for reducing the contact resistances and gate capacitances, which uplift the microwave characteristics of the MOS-HEMT The enhancementmode GaN MOS-HEMTs showed an outstanding performance with a threshold voltage of 1.07 V, maximum extrinsic transconductance of 1438 mS/mm, saturation current at VGS ¼ V of 1.5 A/mm, maximum current of 2.55 A/mm, unity-gain cut-off frequency of 524 GHz, and with a record maximum oscillation frequency of 758 GHz The power performance characterized at 10 GHz to give an output power of 29.6 dBm, a power gain of 24.2 dB, and a power-added efficiency of 43.1% Undoubtedly, these results place the device at the forefront for high power and millimeter wave applications © 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Enhancement-mode MOS-HEMT High-k TiO2 Regrown source/drain TCAD Introduction GaN-based high electron mobility transistors (HEMTs) are the most preferred devices for high-power and high frequency applications, due to their suitable material properties such as high breakdown voltage, high saturation velocity, low effective mass, high thermal conductivity and high two-dimensional electron gas (2DEG) density of the order of 1013 cmÀ2 at the hetero interface [1e3] However, Schottky gate transistors usually exhibit a high gate leakage current [4], and a drain current collapse when operating at high frequencies These are the major factors that limit the performance and reliability of HEMT in radio frequency (RF) power applications Metal oxide semiconductor HEMTs (MOS-HEMTs) with an insulating dielectric is widely investigated, and excellent performance is demonstrated utilizing Al2O3 [4,6], TiO2 [7e9], HfO2 [10,11], Pr2O3 [12,13], SiN [14], SiO2 [14] and NiO [15] as the gate * Corresponding author Laboratory of Semiconducting and Metallic Materials, University of Mohamed Khider Biskra, Algeria E-mail addresses: zinouu113@yahoo.fr (T Zine-eddine), hamaiziaz@gmail.com (H Zahra), messaimr@yahoo.fr (M Zitouni) Peer review under responsibility of Vietnam National University, Hanoi dielectric to overcome the aforementioned limitation These solutions, however, were performed at the expense of a decrease in the device transconductance (gm) and large shift in the threshold voltage (Vth) The dielectric with high permittivity (high k) can effectively alleviate these problems All these devices suffered from the high contact resistance of >0.3 U mm and the high on-resistance of >1 U mm due to the alloyed ohmic contacts and the large source-drain distance Recently, the heavily doped n ỵ GaN source/drain ohmic contacts allowed a significant reduction of the contact resistivity in the proposed device [16,17] The T-gate structure reduces the gate access resistance by providing a large gate area while maintaining the smaller gate length and reduces the extrinsic gate capacitance [18] Also, most of the developed AlGaN/GaN based HEMTs [19] and MOS-HEMTs [17] are the depletion type due to their unique material properties leading to spontaneous and piezoelectric polarizations for two-dimensional electron gas (2DEG) formation [19] Although these types of devices were used in microwave power amplifiers, low noise and RF switching devices, enhancementmode MOS-HEMTs [17,20] have added a more advantage in simpler circuit design and low power consumption due to the elimination of negative power supply [17] which is suitable for the radio frequency integrated circuit (RFIC) design In this paper, we https://doi.org/10.1016/j.jsamd.2019.01.001 2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 181 propose a novel enhancement-mode GaN MOS-HEMT with a 10 nm T-gate length and a high-k TiO2 gate dielectric, This device could be placed at the forefront for high power and millimeter wave applications Device description and simulation models 2.1 The oxide choice The TiO2 is our choice of the high-k dielectric gate material The other high-k materials are shown in Table with their properties [21] Among the gate dielectric materials, TiO2 is considered as the most suitable candidate because of its large static dielectric constant (k ¼ 80e170) TiO2 can increase the physical thickness of the dielectric while maintaining the same oxide capacitance, consequently reducing the leakage current Previous research work [22e24] demonstrated that transistors with TiO2 as gate dielectric had a high breakdown voltage and very low gate leakage current, accompanied by a slight decrease in transistor transconductance and small shift in threshold voltage Fig Cross-section structure of the proposed GaN MOS-HEMT Fig Interface charges and interface traps in GaN MOS-HEMT 2.2 The structure of device Fig shows the cross-sectional schematic of the enhancement (E)-mode GaN MOS-HEMT device with a 10 nm gate-length and source/drain regrowth A 3-inch 4H-SiC is used as a substrate to achieve the good thermal stability The source/drain length is 500 nm The source-gate and the gate-drain spacing are both 645 nm The oxide thickness is nm with a TiO2 dielectric to minimize the leakage Looking at the structure from bottom to top, an AlN nucleation layer is inserted to reduce the stress and the lattice mismatch The undoped GaN channel is 800 nm thick Doped with 2.5  1018 cmÀ3 donors, the Al0.3Ga0.7N of 20 nm thickness constitutes the barrier layer which depletes the 2DEG and provides a strong carrier confinement in the quantum well at the heterointerface and minimizes junction leakage and off-state leakage current Iof and a 5-nm GaN cap layer Next, two graded n ỵ GaN (12 nm), doped with  1019 cmÀ3#donors, are created for the source and drain to reduce the access and contact resistances [16] Non-alloyed contacts are formed for the source/drain regions, which have been shown to give a low contact resistance In a real device, charges exist in all the three interfaces as shown in Fig In the simulation, the polarization charge densities were modelled as fixed interface charge densities The spontaneous and piezoelectric polarization charges of AlGaN and GaN layers were calculated using equations (1)e(9), [25,26] The calculated polarization charge densities at the TiO2/GaN, GaN/AlGaN and AlGaN/ GaN interfaces are displaying in Fig Also, the TiO2/GaN interface is full of dislocations and traps [27] A donor concentration of 8.7  1012 cmÀ2 at the TiO2/GaN interface is considered The total amount of the polarization induced sheet charge density for an undoped AlxGa1-xN/heterostructure can then be calculated by using the following equations:    P ðAl Ga Nị ỵ PSP Alx Ga1x Nị   jsxịj ẳ  PE x 1Àx  PSP ðGaNÞ (1)   &  að0Þ À aðxÞ C13 ðxÞ  2 e xị ỵ e xị 13 33  axị C33 xị  jsxịj ẳ      ỵP xị À P ð0Þ (2) SP SP where a(x) is lattice constant: axị ẳ 0:077x ỵ 3:189ị1010 (3) a0ị ẳ aGaN (4) and c13, c33 are the elastic constants, e33 and e31 are the piezoelectric constants given as follows: c13 ðxÞ ẳ 5x ỵ 103ị (5) c33 xị ẳ 32x ỵ 405ị (6) e13 xị ẳ 0:11x 0:49ị (7) e33 xị ẳ 0:73x ỵ 0:73ị (8) The spontaneous polarization of AlxGa1-xN is also a function of the Al mole fraction x and is given by: Table High-k dielectric materials and their properties [21] TiO2 is the material choice in this research Gate dielectric Material Dielectric constant (k) Energy bandgap Eg (eV) Conduction band offset DEc (eV) Valence band offset DEc (eV) SiO2 Al2O3 TiO2 ZrO2 HfO2 3.9 80 25 25 8.8 3.5 5.8 5.8 3.5 1.1 1.4 1.4 4.4 4.7 1.3 3.3 3.3 Bold represents TiO2 is the material choice in this research 182 T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 PSP xị ẳ 0:052x 0:029ị (9) We consider: Eg (A1N) ẳ 6.08 eV, Eg (GaN) ¼ 3.55eV [31] and the bowing parameter b ¼ 1.3 eV [32] at 300K The electron affinity is calculated such that the band edge offset ratio is given by [33]: DEc 0:7 ¼ DEv 0:3 2.3 Physical models (18) Simulations were performed using Two dimensional (2D) simulations of Silvaco ATLAS TCAD tool The Boltzmann transport theory has shown that the current densities in the continuity equations may be approximated by a drift-diffusion model (DD) This model is one of the most basic carrier transport model in semiconductor physics In this case, the current densities for electrons and holes under the DD model are expressed by the equations: The electron affinity as a function of composition fraction x is expressed as: ! J n ¼ Ànqmn V∅n (10) ! J p ¼ Ànqmp V∅p The nitride density of states masses as a function of composition fraction, x, is given by linear interpolations of the values for the binary compounds [30]: (11) where n and p are electron and hole concentrations respectively, mn and mp are the electron and hole mobility respectively, Fn and Fp are the electron and hole quasi-fermi potentials, respectively The Poisson equation (12), the electron continuity equation (13) and the hole continuity equation (14), based on DD model, are numerically solved [28] A drift-diffusion model is used to solve the transport equation divVJị ẳ r (12) dp ! ẳ VJn ỵ Gp Rp dx q 0:909 103 T T ỵ 830 1:799 103 T Eg AlNị ẳ 6:23 T ỵ 1462 AlxGa1x Nị ẳ 8:5x ỵ 8:91 xị (20) me AlxGa1x Nị ẳ 0:314x ỵ 0:21 xị (21) mh AlxGa1x Nị ẳ 0:417x ỵ 1:01 xị (22) The recombination rate is given by the following expression [34,35]: USRH ¼  n:p À n2i  i h i h Etrap E n ỵ ni exp KT ỵ tn p ỵ ni exp KTtrap L L (23) (14) m0 T; Nị ẳ mmin (15)  T b2  mmax mmin ị 300 T b1 ỵ T b4 h 300 ị T b3 ia300 ỵ Nref 300 (24) where T is the temperature, Nref is the total doping density, and a, b1, b2, b3, b4, mmin and mmax are parameters that are determined from Monte Carlo simulation [36] Another model used for high field mobility, it is based on an adjustment to the Monte Carlo data for bulk nitride, which is described by the following equation [36]: n mn Eị ẳ E m0 T; Nị ỵ ysat n E n1  n2 1ỵa E Ec ỵ  cn1 E Ec (25) The parameters used in the simulation are shown in Table Simulation results and discussion 3.1 Energy band diagram of MOS-HEMT (16) Then, the band-gap energy dependence of the AlxGa1-xN ternary on the composition fraction x using Vegard Law is described, where b is the bowing parameter: Eg ðAlx Ga1Àx NÞ ẳ xEg AlNị ỵ xịEg GaNị bx1 À xÞ The permittivity of the nitrides as a function of composition fraction x is given by [25]: (13) The continuity equations for electrons and holes are defined by ! ! equations (13) and (14), respectively, J n and J p are the current densities for electrons and holes, Gn and Gp are the electron and hole generation rates, Rn and Rp are the electron and hole recombination rates, respectively, q is the magnitude of electron charge [29] The basic band parameters for defining heterojunctions in Blaze (one of the TCAD modules) are the bandgap parameter, the electron affinity, the permittivity and the conduction and valence band density of states [29] Generally, the bandgap for nitrides is calculated in a two-step process: First, the bandgap of the relevant binary compounds is computed as a function of temperature (T) using [30]: Eg GaNị ẳ 3:507 (19) where Etrap is the difference between the trap energy level and the intrinsic Fermi level, TL is the lattice temperature andtn, tpare the electron and hole lifetimes The low-field mobility is modeled by an expression similar to that proposed by CaugheyThomas [36]: whereε is the permittivity, Jis the electrostatic potential and r is the space charge density dn ! ¼ V J n ỵ Gn R n dx q cAlGaNị ẳ cGaNị 1:89x ỵ 0:91x1 xị (17) Fig illustrates the conduction bands in the E-mode GaN MOSHEMT under the gate electrode at zero gate bias This band diagram is used to explain the 2DEG channel formation in the GaN MOS-HEMT The discontinuity in the bandgap, between the AlGaN and GaN gives rise to a band bending process at the interface The band bending is in such a way that the conduction band of the GaN falls below the Fermi level (Ef) and forms a well at the interface T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 Table Electrical and thermal parameters used in this work at 300 K [29,37] Material GaN Band Parameters Epsilon 9.5 Eg (eV) 3.55 Chi (eV) 3.05 Nc(per cc) 1.07e18 Nv(percc) 1.16e19 Effective Richardson Constants An** 14.7 Ap** 71.8 Thermal Velocities (cm/s) 3.34e7 1.51e7 vp (cm/s) Saturation Velocities vsatn (cm/s) 1.9e7 vsatp (cm/s) 6.44e6 Mobility parameters me (cm2/V.s) 1350 mh (cm2/V.s) 13 AlGaN AlN SiC-4H 9.55 3.87 2.69 2.07e18 1.16e19 8.5 6.08 1.01 2.07e18 1.16e19 9.7 3.23 3.2 1.66e19 3.3e19 22.8 71.8 22.8 71.8 91.3 144 2.68e7 1.51e7 2.68e7 1.51e7 1.34e7 1.07e7 1.1e7 6.01e6 1.4e7 6.01e6 2.2e7 1e7 985.5 13.3 1280 14 460 124 183 sheet charge, which can be controlled by varying the alloy composition in the AlGaN layer Equation (26) also shows that the sheet carrier concentration can be increased if the AlGaN layer thickness is reduced and/or the Schottky barrier height is increased [25] The following approximations can be used in equation (26) to calculate the sheet carrier concentration of the 2DEG at the AlGaN/ GaN interface with varying Al mole composition in the AlGaN layer (x) [26] Dielectric Constant: xị ẳ 0:5x ỵ 9:5 (27) Schottky Barrier: e4b ẳ 1:3x ỵ 0:84ị (28) Fermi Energy: EF xị ẳ E0 xị ỵ ph2 mðxÞ ns ðxÞ (29) whereE0 ðxÞis the ground state sub band level of the 2DEG, which is given by: ( 9phe2 ns xị p 80 8mxịxị E0 xị ẳ )2=3 (30) where the effective electron mass, ðxÞx0:22me Band Offset: DEC ẳ 0:7 Eg xị Eg 0ị [26,38] This well is called the quantum well, and the electron inside the well obeys the electron wave characteristics The large band discontinuity associated with strong polarization fields in the GaN and AlGaN allows a large 2DEG concentration to be formed in the device The electron scattering associated with the impurities is less in this region because of the absence of doping in the GaN channel [39] The sheet electron concentration can be calculated using [40]: e  À  ε0 xị ẵe4b xị ỵ EF xị DEC xị dAlGaN e 3.2 DC results The IDS-VDS curves of Fig allowed the evaluation of MOSHEMT characteristics such as the knee voltage (transition between the linear and saturation region), the on-resistance, the maximum current and self-heating (26) The meaning of parameters used in this equation is described and listed in Table It is understood that the sheet carrier concentration is mainly controlled by the total polarization induced Table Parameters of equation (26) [25] Parameters Definition εðxÞ dAlGaN fb ðxÞ EF ðxÞ DEC ðxÞ e Relative Dielectric Constant of AlxGa1-xN Thickness of AlGaN layer Schottky Barrier Height of gate contact on top of AlGaN Fermi level w.r.t the conduction band energy level Conduction band offset at the AlGaN/GaN interface Electronic charge 2,5 Drain current (A/mm) sðxÞ (31) From the simulation, the 2DEG density at the AlGaN/GaN interface is 9.21  1012 cmÀ2 This value is about 15% smaller than the experimental measurements using room-temperature Hall measurement It is reported in the literature that the sheet carrier concentration between experimental measurement and theoretical calculation can differ by ±20% Therefore, the 2DEG densities from the simulation can be accepted to agree reasonably well with the experimental values [25,41] Fig Energy band of GaN MOS-HEMT under the gate electrode nðsÞ ðxÞ ¼ à VGS=3V 2,0 VGS=2V 1,5 1,0 VGS=1V 0,5 VGS=0V VGS=-1V 0,0 Drain voltage (V) Fig IDS-VDS characteristics of the simulated GaN MOS- HEMT 184 T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 Drain current (A/mm) As can be seen in Fig 4, for IDS-VDS characteristics, the gate voltage varied from À1 V to V and drain voltage varied from V to V The device exhibited a peak current density of ~1.5 A/mm at VGS ¼ V and 2.5 A/mm at VGS ¼ V The MOS-HEMT is pinched-off completely at VGS ¼ À1V In Fig (a) the threshold voltage VTH is about 1.07 V The transconductance gm shown in Fig (b) is calculated from the derivative of IDS-VGS 4,0 VDS=5V 3,5 VDS=3.5V VDS=2.5V 3,0 (a) 3.3 Gate leakage performance 2,5 2,0 1,5 1,0 0,5 0,0 -1 Gate Voltage(V) 1,6 Fig shows a comparison of the gate leakage performance of the HEMTs and E-mode GaN MOS-HEMTs with the same device dimensions The leakage current of MOS-HEMTs is found to be significantly lower than that of the Schottky gate HEMTs The gate leakage current density of MOS-HEMTs is almost 3e5 orders of magnitude lower than that of the HEMTs Such a low gate leakage current should be attributed to the large band offsets in the TiO2/ HEMT and a good quality of both the reactive-sputtered TiO2 dielectric This leads to an increase of the two-terminal reverse breakdown voltage (about 25%) and of the forward breakdown (b) 1800 VDS=5V 1,4 VDS=2.5V 1,2 [44] 1600 VDS=3.5V Transconductance (mS/mm) Transconductance (S/mm) curves at fixed VDS and is expressed in Siemens The peak extrinsic transconductance was ~1438 mS/mm Fig illustrates the transconductance verses gate length characteristics of the GaN MOS-HEMTs It reduces the transconductance from 1430 mS/mm to 1258 mS/mm with the gate length change from 10 nm to 60 nm Fig displays the reference of gm versus Lg of our E-mode devices against some state-of-the-art results reported in the literature based on various technologies Obviously, a more balanced, DC performance is achieved in our work which is highly desirable not only for high power applications but for high frequency applications 1,0 0,8 0,6 0,4 This work 1400 [46] 1200 1000 800 [42] [45] 600 [43] 400 0,2 0,0 -1 Gate voltage (V) 20 40 Fig (a) Transfer characteristic, (b) transconductance at VDS ¼ 2.5 V, 3.5 V and5 V 60 80 Gate length (nm) 100 Fig Comparison of extrinsic peak gm VS Lg with the state-of-the-art results reported for GaN-HEMT technology [42e46] VDS=5V Without TiO2 With TiO2 0,01 Gate current (A/mm) Transconductance (mS/mm) 1400 0,1 1300 1200 1100 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 1E-10 1E-11 1000 10 20 30 40 Gate lenth (nm) 50 60 Fig Transconductance with respect of gate length of GaN MOS-HEMT 1E-12 -8 -6 -4 -2 Gate voltage (V) Fig Gate leakage currents for the E-mode GaN HEMT and MOS-HEMT T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 voltage (about 30%) This confirms that the TiO2 dielectric thin film acts as an efficient gate insulator 3.4 Microwave results The high frequency performance of microwave devices can be evaluated through S-parameters simulations The simulations of this type are referred to as small signal due to the relatively small input signal level used for characterization There are several useful pieces of information that can be extracted about the device characteristics from S-parameters simulations Cut off frequency fT and maximum oscillation frequency fmax represent important figures of merit concerning the frequency limits of the device fT is defined as the frequency where forward current gain (H21) from hybrid parameters becomes unity and fmax is defined as the frequency where unilateral gain (Ug) or maximum stable gain (MSG) becomes unity [4] The gains h21, Ug and MSG were extracted directly from simulated S-parameters by the following equations     À2 S21  H21 ẳ  S11 ị ð2 À S22 Þ À S12  S21  (32) jS21 j2    À jS11 j2  À jS22 j2 (33) Ug ¼  MSG ¼  qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  À Á  K± K2 À jS21 j2 jS12 j (34) 185 The small-signal parameters (Table 4) are extracted at the bias of the maximum ft A higher intrinsic transconductance and lower gate parasitic capacitance and resistance are expected to lead to higher RF performance Table compares the small-signal equivalent circuit parameters between this work and other experimental works These results shown that the proposed E-mode GaN MOSHEMT is a promising device for future high speed and highpower millimeter wave RF applications The relationship between the MOS-HEMT gate length and the frequency is shown in Fig 10 It can be seen that ft and fmax increase steadily with the decrease of gate length Lg The gate source capacitance and gate-drain capacitance decrease steadily with the decrease of the gate length We can see that the decrease of gate source capacitance Cgs and gate drain capacitance Cgd, ft and fmax will increase steadily from equations (36) and (37) Therefore, we should decrease gate length under permission of technology when designing E-mode GaN MOS-HEMT ft ¼ gm 2pCgs ỵ Cgdị (36) ft fmax ẳ p Ri ỵ Rs ỵ Rdịgds ỵ 2pFtịRgCgd (37) The comparison of our simulation result with various experimental and simulation results for different gate lengths is depicted in Fig 11 GaN MOS-HEMT in [50]exhibited an ft of 405 GHz but the obtained power gain cut-off frequency is 200 GHz only In this work the proposed E-mode GaN MOS-HEMT shows a ft/fmax ¼ 524/ 758 GHz These high cut-off frequencies with improved drain current density and record transconductance (gm) show that the with Kẳ jS11 j2 jS22 j2 ỵ jS11 S22 À S12 S21 j2 (35)  jS12 j2  jS22 j2 where K is the stability factor Fig displays the small signal characteristics of the same MOSHEMT device with a bias voltage VGS ¼ 1.25 V and VDS ¼ V ft and fmax can be determined based on this graph; fT is the frequency value where h21 becomes dB and fmax is the frequency where Ug or MSG becomes dB [47] fT and fmax were determined to be 524 GHz and a record of maximum oscillation frequency (fmax) of 758 GHz Table Small-signal equivalent circuit model parameters Gate length (nm) gm (mS/mm) gd (S/mm) Cgs (fF/mm) Cgd(fF/mm) Ri (U.mm) Rg (U.mm) Rs (U.mm) Rd (U.mm) Ft (Ghz) Fmax (Ghz) This work [46] [48] [49] 10 1430 0.385 317 121 0.13 0.33 0.04 0.14 522 750 20 1252 0.245 312 107 0.04 0.37 0.05 0.12 453 487 20 1620 0.149 551 106 0.04 0.36 0.11 0.18 354 501 80 620 60 810 361 0.8 e 0.8 1.0 60 127 50 H21 800 Ug 40 Fmax 700 Ft Ft/Fmax (Ghz) Gains (dB) 600 30 20 Fmax=758 Ghz 10 1E9 Ft=524 Ghz 1E10 1E11 Frequency (Hz) 500 400 300 200 1E12 Fig Small signal characteristics for GaN MOS-HEMT at the bias point VGS ¼ 1.35 V and VDS ¼ V 100 10 20 30 40 Gate length (nm) 50 60 Fig 10 The relationship between GaN MOS-HEMT gate length and Ft/Fmax 186 T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 same in case for VGS ¼ 3V biasing These results show the potential for GaNMOS-HEMT to produce millimeter wavelength power 800 This work 700 Fmax Ft/Fmax (Ghz) Ft Conclusion 600 500 [48] 400 [50] [45] 300 [44] [50] [42] 200 100 20 40 60 Gate length (nm) 80 100 Fig 11 Comparison of extrinsic peak ft/fmax vs Lg with the state-of-the-art results reported for GaN-HEMT technology [42,44,45,48,50] proposed GaN MOS-HEMT is a promising device for future high speed and high-power millimeter wave RF applications The Power performance of the GaN MOS-HEMTs were characterized at 10 GHz Fig 12 presents the typical output power and Power Added Efficiency (PAE) results of the device Table lists the power characteristics of the simulated GaN MOSHEMT for various bias conditions Biasing at VGS ¼ V and V can be classified as class A and AB operation At the bias of VGS ¼ V & VDS ¼ 10 V (class AB), a linear gain of 23.3 dB, maximum output power of 29,4dBm (882 mW/mm) and maximum PAE of 42.7% were obtained With higher VGS ¼ V and VDS ¼ 10V (class A), higher linear gain of 24.2 dB, higher maximum output power of 29.6 dBm (921 mW/mm) and lower maximum PAE of 41.2% were achieved At VGS ¼ 2V, the maximum output power increased (from 882 mW/mm to 909 mW/mm) with increased VDS (from 10V to 15V), which is the 35 Gain Pout PEA 50 40 25 20 30 15 20 PEA(%) Pout(dBm) Gain(dB) 30 10 10 0 -20 -15 -10 -5 10 15 20 Pin(dBm) Fig 12 Powercharacteristics, (Pout, Gain and PAE) of the TiO2/AlGaN/GaN MOS-HEMT at 10 GHz Table Power characteristics under various bias conditions VGS VDS Pout Density (mW/mm) Max PEA (%) Linear gain (dB) 3V 3V 2V 2V 10V 15V 10V 15V 921 962 882 909 41.2 42.1 42.7 43.1 24.2 23.9 23.3 22.9 The objective of this paper was to design and simulate a new Emode GaN MOS-HEMT with 10 nm gate-length and with a high-k TiO2 gate dielectric and regrown source/drain The very encouraging results were obtained compared to other works The high cut-off of 524 GHz and with a record of maximum oscillation frequencies of 758 GHz were achieved This is the best E-mode GaN MOS-HEMT high-frequency performance reported to date Moreover, the present MOS-HEMT design is superior to other lately published GaN TiO2-dielectric MOS-devices It is suitable for highpower RF circuit applications References [1] K Jena, R Swain, T Lenka, Impact of oxide thickness on gate capacitanceeModelling and comparative analysis of GaN-based MOSHEMTs, Pramana 85 (2015) 1221e1232 [2] S.-i Takagi, A Toriumi, Quantitative understanding of inversion-layer capacitance in Si MOSFET's, IEEE Trans Electron Dev 42 (1995) 2125e2130 ~ iguez, Compact charge-based [3] F.M Yigletu, S Khandelwal, T.A Fjeldly, B In physical models for current and capacitances in AlGaN/GaN HEMTs, IEEE Trans Electron Dev 60 (2013) 3746e3752 [4] Z e Touati, Z Hamaizia, Z Messai, DC and RF characteristics of AlGaN/GaN HEMT and MOS-HEMT, in: 2015 4th International Conference on Electrical Engineering (ICEE), 2015, pp 1e4 [6] R Swain, K Jena, T.R Lenka, Oxide interfacial charge engineering towards normally-off AlN/GaN MOSHEMT, Mater Sci Semicond Process 53 (2016) 66e71, 10 [7] Z Dong, J Wang, C.P Wen, D Gong, Y Li, M Yu, et al., High breakdown AlGaN/ GaN MOSHEMT with thermal oxidized Ni/Ti as gate insulator, Solid State Electron 54 (2010) 1339e1342 [8] C.-C Hu, M.-S Lin, T.-Y Wu, F Adriyanto, P.-W Sze, C.-L Wu, et al., AlGaN/ GaN metaleoxideesemiconductor high-electron mobility transistor with liquid-phase-deposited barium-doped as a gate dielectric, IEEE Trans Electron Dev 59 (2012) 121e127 [9] K.-T Lee, C.-F Huang, J Gong, C.-T Lee, High-performance 1-GaN n-MOSFET with MgO/MgOestacked gate dielectrics, IEEE Electron Device Lett 32 (2011) 306e308 [10] C.-S Lee, Y.-H Liao, B.-Y Chou, H.-Y Liu, W.-C Hsu, Composite HfO2/Al2O3dielectric AlGaAs/InGaAs MOS-HEMTs by using RF sputtering/ozone water oxidation, Superlattice Microst 72 (2014) 194e203, [11] Y Liu, J Li, W Li, Q Liu, Y Yang, Y Li, et al., Enhanced photoelectrochemical performance of WO3 film with HfO2 passivation layer, Int J Hydrogen Energy 40 (2015) 8856e8863, 8/3 [12] H.-C Chiu, C.-W Yang, Y.-H Lin, R.-M Lin, L.-B Chang, K.-Y Horng, Device characteristics of AlGaN/GaN MOS-HEMTs using high-praseodymium oxide layer, IEEE Trans Electron Dev 55 (2008) 3305e3309 [13] C.-W Lin, C.-W Yang, C.-H Chen, C.-K Lin, H.-C Chiu, Device performance of AlGaN/GaN MOS-HEMTs using La O high-k oxide gate insulator, in: 2009 Proceedings of the European Solid State Device Research Conference, 2009, pp 435e439 [14] C.-H Hsu, W.-C Shih, Y.-C Lin, H.-T Hsu, H.-H Hsu, Y.-X Huang, et al., Improved linearity and reliability in GaN metaleoxideesemiconductor highelectron-mobility transistors using nanolaminate La2O3/SiO2 gate dielectric, Jpn J Appl Phys 55 (2016) 04EG04 [15] D Meng, S Lin, C.P Wen, M Wang, J Wang, Y Hao, et al., Low leakage current and high-cutoff frequency AlGaN/GaN MOSHEMT using submicrometerfootprint thermal oxidized TiO 2/NiO as gate dielectric, IEEE Electron Device Lett 34 (2013) 738e740 [16] S Dasgupta, D.F Brown, F Wu, S Keller, J.S Speck, U.K Mishra, Ultralow nonalloyed ohmic contact resistance to self aligned N-polar GaN high electron mobility transistors by in (Ga) N regrowth, Appl Phys Lett 96 (2010) 143504 [17] T Huang, Z.J Liu, X Zhu, J Ma, X Lu, K.M Lau, DC and RF performance of gatelast AlN/GaN MOSHEMTs on Si with regrown source/drain, IEEE Trans Electron Dev 60 (2013) 3019e3024 [18] X.W Zhang, K.J Jia, Y.G Wang, Z.H Feng, Z.P Zhao, AlNGaN HEMT T-gate optimal design, in: Applied Mechanics and Materials, 2013, pp 1790e1792 [19] U.K Mishra, P Parikh, Y.-F Wu, AlGaN/GaN HEMTs-an overview of device operation and applications, Proc IEEE 90 (2002) 1022e1031 [20] J Wu, W Lu, K Paul, Normally-OFF AlGaN/GaN MOS-HEMT with a two-step gate recess, in: Electron Devices and Solid-State Circuits (EDSSC) IEEE International Conference on, 2015, 2015, pp 594e596 [21] G.D Wilk, R.M Wallace, J Anthony, High-k gate dielectrics: current status and materials properties considerations, J Appl Phys 89 (2001) 5243e5275 T Zine-eddine et al / Journal of Science: Advanced Materials and Devices (2019) 180e187 [22] B.-Y Chou, C.-S Lee, C.-L Yang, W.-C Hsu, H.-Y Liu, M.-H Chiang, et al., TiO 2dielectric AlGaN/GaN/Si metal-oxide-semiconductor high electron mobility transistors by using nonvacuum ultrasonic spray pyrolysis deposition, IEEE Electron Device Lett 35 (2014) 1091e1093 [23] C.-S Lee, W.-C Hsu, B.-Y Chou, H.-Y Liu, C.-L Yang, W.-C Sun, et al., Investigations of TiO 2eAlGaN/GaN/Si-passivated HFETs and MOS-HFETs using ultrasonic spray pyrolysis deposition, IEEE Trans Electron Dev 62 (2015) 1460e1466 [24] H Liu, C Lee, W Hsu, T Wu, H Huang, S Chen, et al., AlGaN/GaN MOS-HEMTs with TiO gate dielectric by using non-vacuum ultrasonic spray pyrolysis deposition, in: 2015 IEEE 11th International Conference on Power Electronics and Drive Systems, 2015, pp 578e580 [25] O Ambacher, B Foutz, J Smart, J Shealy, N Weimann, K Chu, et al., Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures, J Appl Phys 87 (2000) 334e344 [26] O Ambacher, J Smart, J Shealy, N Weimann, K Chu, M Murphy, et al., Twodimensional electron gases induced by spontaneous and piezoelectric polarization charges in N-and Ga-face AlGaN/GaN heterostructures, J Appl Phys 85 (1999) 3222e3233 [27] D.M Zhernokletov, M.A Negara, R.D Long, S Aloni, D Nordlund, P.C McIntyre, Interface trap density reduction for Al2O3/GaN (0001) interfaces by oxidizing surface preparation prior to atomic layer deposition, ACS Appl Mater Interfaces (2015) 12774e12780 [28] T.L SEOW, Study of Trapping Effects in Algan/Gan Moshemts, 2015 [29] SILVACO, Atlas User's Manual DEVICE SIMULATION SOFTWARE, vol 1, 2014 [30] I Vurgaftman, J Meyer, L Ram-Mohan, Band parameters for IIIeV compound semiconductors and their alloys, J Appl Phys 89 (2001) 5815e5875 [31] P.G Moses, M Miao, Q Yan, C.G Van de Walle, Hybrid functional investigations of band gaps and band alignments for AlN, GaN, InN, and InGaN, J Chem Phys 134 (2011) 084703 €pler, [32] H Angerer, D Brunner, F Freudenberg, O Ambacher, M Stutzmann, R Ho et al., Determination of the Al mole fraction and the band gap bowing of epitaxial Al x Ga 1À x N films, Appl Phys Lett 71 (1997) 1504e1506 [33] J Piprek, Semiconductor Optoelectronic Devices: Introduction to Physics and Simulation, Academic Press, 2013 [34] R.N Hall, Electron-hole recombination in germanium, Phys Rev 87 (1952) 387 [35] W Shockley, W Read Jr., Statistics of the recombinations of holes and electrons, Phys Rev 87 (1952) 835 [36] M Farahmand, C Garetto, E Bellotti, K.F Brennan, M Goano, E Ghillino, et al., Monte Carlo simulation of electron transport in the III-nitride wurtzite phase materials system: binaries and ternaries, IEEE Trans Electron Dev 48 (2001) 535e542 [37] N Braga, R Mickevicius, R Gaska, X Hu, M Shur, M.A Khan, et al., Simulation of hot electron and quantum effects in AlGaN/GaN heterostructure field effect transistors, J Appl Phys 95 (2004) 6409e6413 187 [38] T Lenka, A Panda, Characteristics study of 2DEG transport properties of AlGaN/GaN and AlGaAs/GaAs-based HEMT, Semiconductors 45 (2011) 650e656 [39] B.K Jebalin, A.S Rekh, P Prajoon, N.M Kumar, D Nirmal, The influence of high-k passivation layer on breakdown voltage of Schottky AlGaN/GaN HEMTs, Microelectron J 46 (2015) 1387e1391 [40] P Asbeck, E Yu, S Lau, G Sullivan, J Van Hove, J Redwing, Piezoelectric charge densities in AlGaN/GaN HFETs, Electron Lett 33 (1997) 1230e1231 [41] Z Liu, G Ng, S Arulkumaran, Y Maung, H Zhou, Temperature-dependent forward gate current transport in atomic-layer-deposited Al O 3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor, Appl Phys Lett 98 (2011) 163501 [42] Y Lv, X Song, H Guo, Y Fang, Z Feng, High-frequency AlGaN/GaN HFETs with f T/f max of 149/263 GHz for D-band PA applications, Electron Lett 52 (2016) 1340e1342 [43] M.-H Mi, X.-H Ma, L Yang, Bin-Hou, J.-J Zhu, Y.-L He, et al., 90 nm gate length enhancement-mode AlGaN/GaN HEMTs with plasma oxidation technology for high-frequency application, Appl Phys Lett 111 (2017) 173502 [44] P Murugapandiyan, S Ravimaran, J William, K.M Sundaram, Design and analysis of 30 nm T-gate InAlN/GaN HEMT with AlGaN back-barrier for high power microwave applications, Superlattice Microst 111 (2017) 1050e1057 [45] K Shinohara, A Corrion, D Regan, I Milosavljevic, D Brown, S Burnham, et al., 220GHz f T and 400GHz f max in 40-nm GaN DH-HEMTs with re-grown ohmic, in: Electron Devices Meeting (IEDM), 2010, IEEE International, 2010, pp 30.1 1e30.1 [46] Y Tang, K Shinohara, D Regan, A Corrion, D Brown, J Wong, et al., Ultrahigh-speed GaN high-electron-mobility transistors with $ f_ {T}/f_ {\mathrm {max}} $ of 454/444 GHz, IEEE Electron Device Lett 36 (2015) 549e551 [47] Z Kourdi, B Bouazza, A Guen-Bouazza, M Khaouani, Side effects in InAlN/ GaN high electron mobility transistors, Microelectron Eng 142 (2015) 52e57 [48] K Shinohara, D Regan, A Corrion, D Brown, Y Tang, J Wong, et al., Selfaligned-gate GaN-HEMTs with heavily-doped nỵ-GaN ohmic contacts to 2DEG, in: Electron Devices Meeting (IEDM), 2012, IEEE International, 2012, pp 27.2 1e27.2 [49] T Huang, C Liu, J Bergsten, H Jiang, K.M Lau, N Rorsman, Fabrication and improved performance of AlGaN/GaN HEMTs with regrown ohmic contacts and passivation-first process, in: Compound Semiconductor Week (CSW)[Includes 28th International Conference on Indium Phosphide & Related Materials (IPRM) & 43rd International Symposium on Compound Semiconductors (ISCS), 2016, 2016, pp 1e2 [50] D Denninghoff, J Lu, E Ahmadi, S Keller, U Mishra, N-polar GaN/InAlN/ AlGaN MIS-HEMTs with 1.89 S/mm extrinsic transconductance, A/mm drain current, 204 GHz f T and 405 GHz f max, in: Device Research Conference (DRC), 2013 71st Annual, 2013, pp 197e198  ... The leakage current of MOS- HEMTs is found to be significantly lower than that of the Schottky gate HEMTs The gate leakage current density of MOS- HEMTs is almost 3e5 orders of magnitude lower than... than that of the HEMTs Such a low gate leakage current should be attributed to the large band offsets in the TiO2/ HEMT and a good quality of both the reactive-sputtered TiO2 dielectric This... Transconductance with respect of gate length of GaN MOS- HEMT 1E-12 -8 -6 -4 -2 Gate voltage (V) Fig Gate leakage currents for the E -mode GaN HEMT and MOS- HEMT T Zine-eddine et al / Journal of Science: