213 74 AlGaN/GaN Influence of metal material on capacitance for Schottky-gated AlGaN/GaN 1, 2, 1, 2, 2, 2, 2, 2, 2, 2, 1, 1 1
AlGaN/GaN デバイス ① GaNの優れた物性値 ② AlGaN/GaN HEMT構造 ワイドバンドギャップ半導体 (3.4eV) 絶縁破壊電界が大きい (3 16 V/cm) 飽和電子速度が速い (2.7 17 cm/s) Thermal Conductivity 5 High Tem. 4 Operation 3 Electric Field High Voltage Operation GaN 2 Si Energy Gap Electron Mobility SiC 1 Yole développement, Power GaN, 212 高い電子移動度 (2cm2/Vs) Schottky metal PSP 2DEG Ec PPE PSP Al.25Ga.75N EF GaN Melting Point Electron Velocity High Frequency Operation ヘテロ界面に2DEG形成 高周波パワーデバイス への利用に期待 2
( Cu ) S G D Al.25 Ga.75 N GaN 2DEG Buffer layer Si (111)Substrate 3
AlGaN/GaN HEMT W Al S G Al.25 Ga.75 N D GaN 2DEG Buffer layer Si (111)Substrate,,W,Al 4
i-al.25 Ga.75 N(25nm)/i-GaN(1µm) on buffer/si(111) SPM and HF cleaning Oxide deposition (plasma-teos) Patterning and BHF for SiO 2 etching Mesa isolation (RIE with Cl 2 ) SPM and BHF for SiO 2 etching Oxide deposition (plasma-teos) Patterning and BHF for S/D contact opening Metal deposition (Sputtering) (5nm)/Al(6nm)/Ti(5nm) /Al /Ti Al.25 Ga.75 N (25nm) GaN(1µm) Buffer layer (1µm) Si(111) Substrate Al.25 Ga.75 N (25nm) GaN(1µm) Buffer layer (1µm) Si(111) Substrate TEOS-SiO 2 /Al /Ti 2DEG AlN (1nm) AlN (1nm) 5
Patterning and RIE with Cl 2 for S/D contact Annealing in N 2 at 95 o C for 3 sec Oxide deposition (plasma-teos) Patterning and BHF for gate opening SPM and HF cleaning Gate metal (,, W, Al) deposition (Sputtering) Gate patterning Contact opening (Buffered HF) Current [A] 6 4 2-2 -4 3sec in N 2 (5nm) /Al(6nm) /Ti(5nm) -6x1-3 -5-4 -3-2 -1 1 2 3 4 5 Voltage [V] /Al /Ti 8µm 3µm Metal 95 o C 5 o C /Al /Ti Al.25 Ga.75 N (25nm) 15µm TEOS-SiO 2 FGA (H 2 : N 2 = 3% : 97%) for 1min Measurement CV,IV,Gp/ω,Current collapse AlN (1nm) GaN(1µm) Buffer layer (1µm) Si(111) Substrate 2DEG 6
Capacitance [pf] 12 1 8 6 4 L / W = 25 / 1µm FGA 3 o C for 1 min 1kHz 1kHz 5kHz 1MHz Capacitance [pf] 12 1 8 6 4 Capacitance [pf] 12 1 8 6 4 W 2 2 2-8 -6-4 -2 Gate Voltage [V] -8-6 -4-2 Gate Voltage [V] -8-6 -4-2 Gate Voltage [V] (-4V) W 1kHz 7
Gate Leakage Current [A/cm 2 ] 1 4 1 2 1 1-2 1-4 1-6 1-8 Al W L / W = 25 / 1µm FGA 3 o C for 1 min -5-4 -3-2 -1 1 Gate Voltage [V] Drain Current [A] 1-2 1-3 1-4 1-5 1-6 1-7 1-8 V ds = 1V V ds =.5V L / W = 25 / 1µm FGA 3 o C for 1 min -7-6 -5-4 -3-2 -1 1 Gate Voltage [V] 8
(x1-8 ).6 G p /ω (S sec/cm 2 ).4.2. Conductance spectra (G p /ω) V g = -6.V -4.4V -6.V V g = -4.4V 1 2 1 3 1 4 1 5 1 6 Frequency (Hz) D it (cm -2 /ev) τ (sec) 1 12 1 11 1-3 1-4 1-5 D it and time constant (τ) -6. -5.5-5. -4.5 Gate voltage (V) (5% )D it ( ) 9
(x1-8 ) G p /ω (S sec/cm 2 ) 1.5 1..5. 1.5 1..5. Conductance spectra (G p /ω) gate gate -3.V -3.2V V g = -4.1V V g = -3.6V 1 2 1 3 1 4 1 5 1 6 Frequency (Hz) D it (cm -2 /ev) τ (sec) 1 12 1 11 1 1 1-3 1-4 1-5 D it and time constant (τ) -4.1-3.9-3.7-3.5-3.3 Gate voltage (V) -3.1 D it 1
g m (S) W/L=1/25µm V d =.5V V g (V) g m g m (AlGaN/GaN ) 11
: (Hole-like traps) : AlGaN 12
2 2 2 Drain Current [ma] Drain Current [ma] 18 16 14 12 1 18 17 16 15 14 13 V gs = 6V L / W = 25 / 1µm FGA 3 o C for 1 min 1 2 3 Drain Voltage [V] V gs = 6V V ds = 1V W 4 Drain Current [ma] 18 16 14 12 1 V gs = 6V L / W = 25 / 1µm FGA 3 o C for 1 min 1 2 3 Drain Voltage [V] Drain Current [ma] 18 16 14 12 1 4 W Reduced I d V gs = 6V L / W = 25 / 1µm FGA 3 o C for 1 min 1 2 3 4 Drain Voltage [V] ( ),W 12 1 2 3 4 5 6 Drain Bias [V] 13
, AlGaN AlGaN AlGaN/GaN (ON ) 14
12 1 Annealing for 1 min L / W = 25 / 1µm 12 1 Annealing for 1 min L / W = 25 / 1µm Capacitance [pf] 8 6 4 3 o C 4 o C 5 o C 6 o C Capacitance [pf] 8 6 4 3 o C 4 o C 5 o C 6 o C 2 at 1 khz (a) -8-6 -4-2 Gate Voltage [V] 2 at 1 khz (b) -8-6 -4-2 Gate Voltage [V]
Gate Leakage Current [A/cm 2 ] 1 4 1 3 Open : at 1 V Solid : at -5 V 1 2 1 1 1 1-1 1-2 1-3 1-4 1-5 1 2 3 4 5 6 7 Annealing Temperature [ o C] 8
g m, max [µs] 5 48 46 44 42 Annealing for 1 min V ds =.5V Reduction in g m, max 4 No FET operation with above 5 o C 38 1 2 3 4 5 6 7 Annealing Temperature [ o C] 8
2DEG at AlGaN/GaN interface Ambacher O. et al., JAP, 85, 3222, 1999. AlGaN P SP P PE Schottky metal P SP P PE 2DEG E c P SP E F GaN P SP Al.25 Ga.75 N GaN P SP : Spontaneous polarization P PE : Piezoelectric polarization 2DEG (~1 13 cm -2 ) are obtained without any doping. High electron mobility transistor (HEMT) is possible.
6 inch AlGaN/GaN substrate
I d -V d characteristics Drain Current [ma] 8 6 4 2 L / W = 25 / 1µm FGA 3 o C for 1 min V gs = V -1V -2V Drain Current [ma] 8 6 4 2 V gs = V -1V -2V Drain Current [ma] 8 6 4 2 W V gs = V -1V -2V -3V -3V -3V 2 4 6 8 Drain Voltage [V] 1 2 4 6 8 Drain Voltage [V] 1 2 4 6 8 Drain Voltage [V] 1 Fabrication and operation of HEMT with,, W Al-gated HEMT : large gate leakage current
Current collapse W. Saito (TOSHIBA), 21/6/24 G. Meneghesso et al., Microelectron. Eng, vol. 19, pp. 257 261, 213. Low Drain Voltage High Drain Voltage Trap are thought to be related to frequency dispersion. Evaluation of current collapse
Current collapse vs. nitrogen Drain Current [ma] 2 15 1 5 2 2 (a) (b) (c) V gs = 6V L / W = 25 / 1µm FGA 3 o C for 1 min Drain Current [ma] 15 1 V gs = 6V 5 L / W = 25 / 1µm FGA 3 o C for 1 min 1 2 3 4 1 2 3 4 1 Drain Voltage [V] Drain Voltage [V] Drain Current [ma] 15 1 Reduced I d (N 2 :Ar=3:7) (N 2 :Ar=2:8) (N 2 :Ar=1:9) V gs = 6V 5 L / W = 25 / 1µm FGA 3 o C for 1 min 2 3 Drain Voltage [V] 4 Current collapse are found to be correlated to nitrogen. Higher nitrogen concentration can suppress the collapse.
Current collapse & C-V characteristics Drain Current [ma] 2 18 16 14 V gs = 6V V ds = 15V (N 2 :Ar=3:7) (N 2 :Ar=2:8) (N 2 :Ar=1:9) Capacitance [pf] 12 1 8 6 4 2 FGA 3 o C for 1 min L / W = 25 / 1µm N 2 :Ar = 1:9 N 2 :Ar = 2:8 N 2 :Ar = 3:7 at 1 MHz 12 1 2 3 4 Drain Bias [V] 5 6-8 -6-4 -2 Gate Voltage [V] Current collapse depend on the nitrogen concentration. Same capacitance indicates no unintended layer.
Gate leakage and I d -V g characteristics Gate Leakage Current [A/cm 2 ] 1 2 1 1 1 1-1 1-2 1-3 1-4 1-5 1-6 N 2 :Ar = 1:9 N 2 :Ar = 2:8 N 2 :Ar = 3:7 L / W = 25 / 1µm FGA 3 o C for 1 min -6-5 -4-3 -2-1 1 Gate Voltage [V] Drain Current [A] 1-3 1-4 1-5 1-6 1-7 1-8 V ds =.5V N 2 :Ar = 1:9 N 2 :Ar = 2:8 N 2 :Ar = 3:7 L / W = 25 / 1µm FGA 3 o C for 1 min -6-5 -4-3 -2-1 Gate Voltage [V] Higher nitrogen concentration provides lower leakage. These results coincide with the use of various metals.
Conclusions Gate metal induce effects has been experimentally investigated with the use of various metals Gate metal strongly affect on the current collapse, gate leakage current and frequency dispersion in C-V characteristics. can suppress the current collapse compared with conventional metal. trogen concentration in are found to be related to the current collapse and gate leakage current. The dependence of the current collapse on nitrogen concentration indicates that the nitrogen defects are origin responsible for the traps.