Modeling and Simulation of Unilateral power gain for GaN/AlGaN HEMT

Transcription

1 IN No: I Vol-4, Issue-4, August 16 Modeling and imulation of Unilateral power gain for GaN/AlGaN HEMT Vidashree.L, PG cholar, Department of Electronics and communication Daananda agar college of Engineering Bangalore, India Dr. P. Vimala Associate Professor, Department of Electronics and communication Daananda agar college of Engineering Bangalore, India Abstract In this paper we have designed the GaN/AlGaN HEMT in Comsol tool and obtained the simulation results of the same structure. The imulation results including the meshing part of GaN HEMT, two dimensional electron gas (DEG between AlGaN and GaN laers and the Drain current characteristics of GaN HEMT for the given Gate and Drain voltages. Also we derived the analtical modelling for RF Characteristics such as unilateral power gain(g u and maximum stabilit gain(g ms based on -Parameters and Y-Parameters for GaN/AlGaN HEMT. The modelling results of Unilateral power gain is simulated using Matlab and compared with the simulation results. II.Analtical Modelling of gain GaN/AlGaN HEMT is as shown in the Fig. 1. It has 5 laers, such as Doped AlGaN laer, AlGaN pacer laer, GaN laer, Nucleation laer and the IC laers. The ome portion of AlGaN is doped to increase the drain current. pacer laer is used to increase the Electron Mobilit in DEG.Above the GaN laer DEG is formed and the AIN nucleation laer is used to match the Crstal structure of GaN with the Crstal structure of IC material. IC can withstand at high thermal operation, hence it is used in GaN/AlGaN HEMT. I. Introduction GaN based HEMT will have more advantages than GaAs based HEMT for its good Breakdown voltage, less power dissipation, abilit to operate at more current and voltages compared to GaAs based HEMT and also The can withstand at High temperature and having more power densit [1-3]. For that purpose, we are discussing about GaN/AlGaN HEMT here. HEMT is designed using GaN and AlGaN emiconductor materials in which the have a different energ bandgap [4]. In between them DEG will be produced in terms of nanometer. This DEG is like a channel in MOFET [5-7]. In this paper we are discussing about the structure of GaN/AlGaN HEMT designed using Comsol tool, we have performed the meshing of the design, analzed DEG and also obtained simulation results such as the Drain current vs Drain voltage (I-V Characteristics, Drain current vs Gate voltage (I-V Characteristics of GaN HEMT. The Applications of GaN/AlGaN HEMT is used in pace applications, Radar and in satellites because of their High efficienc, High Power and High Frequenc applications [8,9]. Generall, HEMT are designed b using either GaAs emiconductor material or GaN emiconductor material. In [1] Analtical modelling of admittance parameters and cattering Parameters are determined for GaN/AlGaN G-HEMT using Two port network concepts. As an extension we have determined the RF Characteristics of GaN/AlGaN HEMT from the obtained -Parameters in [1]. RF characteristics results are compared with the simulation results []. Fig 1: GaN/AlGaN HEMT structure designed in Comsol tool In [1] considered the mall signal equivalent circuit of GaN based HEMT. The EC of GaN HEMT is as shown in Fig.. The HEMT is having 3-Terminals, source, drain and gate. Intrinsic parameters(y-parameter can be find out b considering the Gate to source Capacitance (C gs, Input Resistance (R i, Gate to drain zcapacitance (C, Output conductance (G d parameters. Y m is the Current source generator and it is alwas equal to g m exp( j. 15

2 IN No: I Vol-4, Issue-4, August 16 In [1], is obtained b Y-Parameter is called as input reflection s-coefficient The ((1 Z(1 Z ( Z 1 (5 ((1 Z (1 Z ( Z is obtained b Y-Parameter is called as 1 Fig : mall ignal Equivalent circuit for HEMT A. Intrinsic Y-Parameter In -port Equivalent circuit of GaN based HEMT, we will get four admittance parameters, the are,, 1,.Each parameter is represented in terms of Real part and imaginar part. Analtical modelling of Y-parameters obtained bellow is the Input admittance parameter which is the ratio of the current at input port to the voltage at input port,when output port is short circuited. i.e j CgsV1 + j C (1 j C R 1 gs i is the Reverse transfer admittance parameter which is the ratio of the current at input port to the voltage at output port, when input port is short circuited. i.e j C ( is the Forward transfer admittance 1 parameter which is the ratio of the current at output port to the voltage at input port, when output port is short circuited. i.e 1 gs i gm exp( j - j C R 1 j C (3 is the output admittance parameter which is the ratio of the current at output port to the voltage at output port, when input port is short circuited. i.e g d j C (4 B. Intrinsic cattering(-parameter -Parameters are used to determine the RF characteristics of GaN HEMT. In this paper we have used the analtical modelling of Y-parameters such as,, 1, to determine the -Parameters such as s, s, s1, s.the bellow expressions shows Intrinsic Y-parameters are converted into Intrinsic -parameters. Reverse Transmission scattering coefficient = Z (1 Z (1 Z ( Z 1 (6 The is obtained b Y-Parameter is called 1 Forward Transmission scattering coefficient Z1 = 1 (1 Z (1 Z ( Z 1 (7 The is obtained b Y-Parameter and is called output reflection scattering coefficient ((1 Z(1 Z ( Z 1 (8 ((1 Z (1 Z ( Z We have compared the Analtical modelling result of Y and -parameters with Matlab tool imulation results. The Parameters used to find out the simulation results are shown in Table 1. In [3] the have done parameter extraction using these values. TABLE 1. LIT OF PARAMETER ANDVALUE UED FOR IMULATION l no. Parameters Name Used Values 1 C (ff 8. C gs (ff.8 3 C ds (ff 3. 4 G ds (ms.1 5 R i (ohm G m (ms R (ohm Tau(ps.41 C. Unilateral Power gain A transistor is said to be unilateral if the signal/power bounced back from the output to the source is equal to. This occurs if the reverse transmission coefficient, or the reverse transducer power gain, is equal to. The forward transmission coefficient 1 is directl related to the maximum transducer power gain of the

3 IN No: I Vol-4, Issue-4, August 16 device given as. Therefore, higher the value of, higher is the power gain obtainable from the device and hence higher is the frequenc of operation. The reverse isolation parameter determines the level of feedback from the output of an amplifier to the input and therefore influences its stabilit together with the forward gain. The analtical results obtained in Vidashree L and Dr. P Vimala, [1], correspond well with the simulated results obtained in Bhattachara et.al []. proving the correctness of the various assumptions taken in the development of its EC. The Unilateral Power Gain (Gu, the highest possible gain that an active port can achieve is plotted for the frequenc range of 1 1 GHz in Fig. 7 and is obtained using an expression [], 1 1 * 1 Gu s (9 K 1 Re( where, 1 K 1 where, 1 1 Fig 3: Meshing of GaN/AlGaN HEMT structure designed in Comsol tool Drain current characteristics of GaN/AlGaN HEMT is as shown in the Fig 4 and Fig 5.In Fig 4 Drain current varies for the given Gate voltges and b making Drain Voltage Constant. Fig 5 shows that Drain current varies for the given Drain voltges b making Gate Voltage Constant. K is the tabilit factor which determines the stabilit of the device. K > 1 and D < 1 forms the primar condition for the device to be stable. Fig. 8 shows Maximum tabili power gain Vs Frequenc(GHZ. The Maximum table Gain of the device is defined as the highest possible value of power-gain that is achieved before the instabilit occurs, i.e., at K = 1 and is obtained using the expression [], 1 G ms (1 Fig 4:Drain Current vs Gate Voltage V-I Characteristics IV. Results and Discussions I. GaN HEMT imulation: Meshing plas an import role in an electronic component or circuit design. we can find thin meshes and the thick meshes. Generall thick meshes are near the boarders of the laer and if the dimensions of the laers are small. Fig 3 shows the meshing of GaN/AlGaN HEMT structure designed in Comsol tool. Fig 5:Drain Current vs Drain Voltage V-I Characteristic 17

4 IN No: I Vol-4, Issue-4, August 16 Fig 6 shows the DEG between AlGaN and GaN materials.algan has higher energ band gap and GaN has low energ band gap.o conduction band of AlGaN will raise to connect to the GaN conduction band.this as shown in the Fig 6.Blue lines are the conduction band,green lines are the valance band and dark black line indicates the fermi level at eqalibrium. Fig 7:Unilateral power gain Vs Frequenc(GHZ Fig 6: DEG obtained for GaN/AlGaN material II. RF Characteristics of GaN/AlGaN HEMT A transistor is said to be unilateral if the signal/power bounced back from the output to the source is equal to. Unilateral power gain alwas depends upon 1 and parameters. Fig 7 shows that Unilateral power gain plotted with respect to frequenc in GHZ. G u is Maximum (4 DB at frequenc 1GHZ.As frequenc increases G u decreases. Fig 8 shows Maximum stabilit gain plotted with respect to frequenc in GHZ. G ms is Maximum (1 DB at frequenc 1GHZ.As frequenc increases G ms decreases. Both Unilateral power gain and Maximum stabilit gain results are compared with Bhattachara et.al []. Fig 8:Max.tabili power gain Vs Frequenc(GHZ CONCLUION mall signal analsis is done and determined the analtical modelling of admittance parameters and Obtained admittance parameters are used to determine the -Parameters. In this paper b using matlab we determined RF Characteristics such as Unilateral power gain and Maximum stabilit gain using -Parameters, and also as a separate part we designed GaN /AlGaN the simulation results such as V-I characteristics and DEG are obtained for GaN/AlGaN semiconductor materials using Comsol tool. REFERENCE 1. Parveen jothika jogi and Mridula gupta, Intrinsic Admittance Parameter for eparate Gate InAlAs/InGaAs DG-HEMT for 1 nm Gate length, IEEE conference, New Delhi, India, ICT 13.. Parveen jothika jogi and Mridula gupta and R. gupta, RF characteristics of 1-nm separate gate InAlAs/InGaAs DG-HEMT, Microwave and optical technolog letters, Vol 55, No., pages 5, November

5 IN No: I Vol-4, Issue-4, August Du jiangfeng, mall signal modelling of AlGaN/GaN HEMT with consideration of CPW Capacitance, IEEE Transaction, Vol 33, No.3, pages 4, march Mazhar B Taer, Parameter Extraction for Pseudo orphic HEMT using Genetic Algorithms, IEEE Transaction, Vol 3, No., published in Ma Teng, Topic, A new small signal model of asmmetric AlGaN/GaN HEMT. Xidian universit, Vol 31, No. 6, june 1 6. Ronan G Brad, An improved small signal parameter extraction algorithm for GaN HEMT devices, IEEE Transaction on microwave and technolog, Volume 56, June Parveen jothika jogi and Mridula gupta Modeling of InAlAs/InGaAs/InAlAs DG- HEMT Mixer for microwave applications. IOR, Vol 1, issue 4,15 8. Niraj and man shresta, imulation stud of AIN spacer laer thickness on AlGaN/GaN HEMT, Himalaan phsics, Vol 4, No.4, K. Feblets, Influence of undoped spacer laer thickness on GaAs/AlGaAs HEMT, emiconductor science technolog, Vol 13, Vidashree L and Dr. P Vimala, Two port network based cattering parameter, Modelling and imulation of GaN/AlGaN HEMT, ICPCIT Conference, Bangalore, India, Ma 16.. M. Bhattachara et. al, scattering parameters based modelling and simulation of mmetric tied gate HEMT for millimetre application, solid state Electronics, New Delhi, Vol 63,.. Kasemsuwan Varakorn, EI Nokali Mahmoud, A microwave model for high electron mobilit transistor, IEEE Transaction MTT,45(3,4-7,