A new approach to determinate parasitic elements of GaN HEMT by COLD FET S-Parameter

Transcription

1 A ne approach to determinate paraitic element of GaN HEMT by COLD FET -Parameter Min Han 1*, Yongheng Dai 1, 2, Jianjun Zhou 2, Chao Liu 3, Xu Li 1 1 chool of Electronic and Optical Engineer,Nanjing Univerity of cience and Technology Xiaolingei 200, Nanjing, China 2 Nanjing Electronic Device Intitute 3 College Of Phyic Engineering, Qufu Normal Univerity *1 hanzhenru@163.com (Received eptember ) Abtract: A implified approach to the paraitic element of 2-gate figure GaN HEMT i introduced by pinch-off COLD FET -Parameter. When extracting the paraitic parameter at pinch-off tate, intrinic circuit can be ignored a no current flo through it. A a reult, if only taking extrinic part into account, equivalent circuit contructed at different frequencie can extract different paraitic element. With paraitic parameter from thi approach, the imulation reult of equivalent circuit agree very ell ith experiment. Keyord: Paraitic element, GaN HEMT, COLD FET -Parameter. doi: /TT Introduction The development of GaN HEMT i very fat in the lat year. Much effort ha been put into developing accurate mall-ignal imulation model for GaN HEMT. It ha been hon [1, 2] that the value of element obtained for the intrinic FET depend on the extrinic one. Thi implie that extrinic element mut be extracted ith a high degree of accuracy. The paraitic element are uually determined from cold FET meaurement. A Diamant and Laviron have uggeted [3], the -Parameter meaurement at zero drain bia voltage can be ued for the evaluation of device paraite becaue the equivalent circuit i much impler. The tandard procedure i baed on the meaured -Parameter. Firt, the -parameter i converted to Y-parameter. Then the Y-Parameter i taken into the extrinic component expreion, the circuit element of the GaN HEMT can then be calculated uing analytical equation. The device ued in thi paper i hon in Fig. 1. It i a 2-figure GaN HEMT made in Nanjing Electronic Device Intitute. 189

2 Fig. 1 Micro photo of 2-finger GaN HEMT 2. Paraitic capacitance Paraitic capacitance i determined by the Y parameter at lo frequencie (<5 GHz) ith cut-off condition (Vd0, Vg<Vth). And the equivalent circuit i hon in Fig. 2. Cgd G D Cgp Cgi Cg Cd Cdi Cdp Fig. 2 The equivalent circuit of lo-frequency cut-off condition (Vd0, Vg<Vth) At lo frequencie, the imaginary part of Y parameter can be expreed a, Im( Y11) j( Cgi + Cgp + Cg + Cgd ) Im( Y12) Im( Y21) jcgd I ( Y ) j( C + C + C + C ) m 22 dp di d gd When GaN HEMT i at pinch-off tatu, the depletion layer i ymmetrical. Moreover, the paraitic capacitance of the electrode i approximately equal. Thu e can ue the folloing approximation, I ( ) m Y12 Cgd Cg (4) Cgp Cdp (5) Im( Y11) + 2 Im( Y12) Cgp Cdp 4 (6) The reult of experiment ho that Cgi and Cdi are mall. Thu they can be approximately (1) (2) (3) 190

3 equal. A a reult, And, C d Im( Y22) Im( Y11) + 2 Im( Y12) (7) C C gi di 3C 3C gp dp (8) (9) 3. Paraitic inductance At lo frequencie (<5 GHz), paraitic inductance and paraitic reitance are extremely enitive to the -Parameter,o it i difficult to extract them accurately. Thu the determination job i operated at high frequencie (>5 GHz). Then the value of paraitic inductance i extracted at the bia point, Vd0, Vg0. Taking into account of the ymmetrical tructure of HEMT device, the equivalent circuit i hon in Fig. 3. Ld G Rg Cg Cd Rd D C R Fig. 3 The equivalent circuit of GaN HEMT at high frequencie hen Vd0 and Vg0 The Z-Parameter of circuit i given by, 1 1 Z11 R + Rg + + jl [ ( + Lg) ] C C 1 Z12 Z21 R + + j[ ] C 1 1 Z22 Rd + R + Rc + jl [ ( + Ld) ] C C g d (10) (11) (12) Beide, 191

4 1 I m( Z12) C (13) It i derived that ωim(z12) and ω2 fit traight line ith a lope of. imilarly, ωim(z22-z11) and ω2 fit traight line ith a lope of Ld. ωim(z11-z12) and ω2 fit traight line ith a lope of Lg. Thu, at high frequencie,, Ld and Lg are hon repectively a folloing, L I ( m Z ) 12 (14) L L d g I ( Z 22) I m m( Z 22 Z 12) I ( Z 11) I m m( Z 11 Z 12) (15) (16) 4. Paraitic reitance To method have been ued to obtain Rd, R and Rg. The firt one i baed on the meaurement of DC characteritic and the econd one i baed on COLD-FET -Parameter [4]. The method preented in thi paper i baed on the -Parameter at zero bia. The equivalent circuit i hon in Fig. 4. Ld G Rg Cg Cd Rd D C R Fig. 4 Equivalent circuit of high frequency (>5 GHz) at zero bia The paraitic reitance R i generated by fitting the real part of Z Parameter. From (10), (11) and (12), 192

5 R ( Z ) R + R + R (17) e 11 g c/2 R ( Z ) R + R (18) e 12 c/2 R ( Z ) R + R + R (19) e 22 c d Combining ith the pinch-off Z-Parameter, e have, ( 12 ) ( 21) ( ) ( ) R R Z R Z (20) e e R R Z + Z R Z R (21) g e e 11 Firt, e take Z-Parameter at zero bia into (17), (18) and (19). econd, e take pinch-off Z-Parameter into (20) and (21), then e can deduce the Rd. We can alo extract paraitic reitance by utilizing the meaured -Parameter by the previouly mentioned approach. 5. Concluion All the value of paraitic element are deduced (Table 1) according to the above dicuion. Then e take thoe value into the equivalent circuit of pinch-off cold device and imulate the circuit in a ide band (from 0 GHz to 20 GHz). We can compare the imulated -Parameter curve ith the meaured -Parameter to verify the conitency. A it can be een in Fig. 5 and Fig. 6,the imulated curve agree ell ith the meaured one in a broad frequency band. A concie approach for determining the paraitic element of a 2-figure GaN HEMT ha been propoed and analyzed. Thi method conit in a direct determination of all the FET paraitic element. The knoledge of thee paraitic element ill help u determine the intrinic mall-ignal parameter. Compared ith the conventional method, the method baed on -Parameter can be ued in a broad frequency range. Tab. 1 The value of paraitic element C dp4.53 ff C gp4.53 ff C di9.62 ff C gi19.73 ff L d36.43 ph L 5.27 ph R g3.89 Ω R d2.32 Ω L g36.43 ph R 2.18 Ω 193

6 Fig. 5 Meaured and imulated 11-Parameter Fig. 6 Meaured and imulated 21-Parameter Acknoledge The author ould like to thank the upport of Defence Key Lab Fund (9140C C1402) Reference [1] Ban-Leong Ooi. Mook-eng-Leong, Pan-hyan Kooi. "A Novel Approach for Determining the GaA MEFET mall-ignal" Equivalent-Circuit Element". IEEE Tran. On Microave Theory and Technique, 45, 12, (1998). 194

7 [2] Kazuo hirakaa, Hideyuki Oikaa, Tohihiro himura, et. al.. "An approach to Determining an Equivalent Circuit for HEMT'". IEEE Tran. On Microave Theory and Technique, 13, 3, (1995). [3] F. Diamant and M. Laviron. Meaurement of the extrinic erie element of a microave MEFET under zero current condition in Proc. 12th European Microave Conf., (1982). [4] W.R.Curtice. "A MEFET Model for Ue in the Deign of GaA Integrated Circuit". IEEE Tranaction on Microave Theory and Technique, 28, 5, (1980). 195