Microwave Devices - Microwave Passive Devices I - 3 2008 / 1 학기 서 광 석

Bottom side 전류가 dominant Attenuation (1)  Attenuation R U V G R – conductor loss c=R/2Zo G – dielectric loss d=GZo/2 Total loss  = c + d + r ( radiation loss ) 1. conductor loss top metal bottom metal x  - edge에 많은 전류 flow - skin depth Skin depth Bottom side 전류가 dominant (top metal)

Attenuation (2) (GaAs MMIC) : Au, W/Au (high cost) Metal의 종류 ( Si IC ) : Al  Cu (large  ) (   RC time constant, delay  ) (GaAs MMIC) : Au, W/Au (high cost)   (largest  , 안정성) (thick) 2. dielectric loss ( ) E1(air), E2 (dielectric) 의 모양이 전체가 air인 경우와 같다고 가정할 때 [Ref. Collin pp.153~155] * ceramic-loaded teflon : 30 GHz 이상에서 loss가 급격히 증가 (laser drilling for via)  quartz for millimeter wave applications

Attenuation (3) 3. radiative loss radiation Ref. ”Handbook of Microwave Integrated Circuits” by R.K.Hoffman conductor–backed dielectric waveguide ( lowest mode : TMo with fc=0 ) leakage - Pradiation  f 2 at f=fs : strong coupling for leakage  ex) h=0.5mm, r=9.6  fs = 60 GHz h=0.1mm, GaAs MMIC  fs ~ 300 GHz

Microstrip Discontinuity (1) Ref. 1. K.C Gupta 2. P.B Katehi et. al IEEE Trans.MTT p.1029 E, H의 연속성을 만족시키기 위해 higher order mode , surface mode, radiation mode등이 excite. 1. open discontinuity Vdc circuit V /4 Open end (bias circuit)

Microstrip Discontinuity (2) open radiation Coc Goc V radiation r Coc Coc Goc Freq. <full-wave analysis> Modified equivalent circuit C Coc , C, L, R = functions of w/h U Coc U U L R V Ref : K. C. Gupta, et al., “Microstrip Lines and Slotlines,” Chap. 3, pp. 182-183. V V

Microstrip Discontinuity (3) 2. gap Coupler에 응용 작은 C 필요 시 응용 <simple model> 3. bend current flow가 작은 영역 - capacitive U  compensated bend Chamfered bend r w r>3 w d s Soptimum/d =0.52+0.65exp(-1.35w/h)

Microstrip Discontinuity (4) 4. other discontinuities U step in width T junction improved T junction w 0.3w 2w or 2h (longer) U 0.7w

Microwave Passive Elements – Resistor (1)  Microwave Passive Elements ----- R , L , C, coplanar, transformer… Ref. “MMIC Design” chap. 3 1. Resistor - impedance matching Zo= 50  (precision) - bias resistor RG ~ 수백  (up to K) RG metal resistor (~50 : precision) t Au GaAs L W R = Rㅁ*L/W = (/t)* L/W precision을 위해서는 W  , L  density를 증가하기위해서는   , t 

Microwave Passive Elements – Resistor (2) NiCr : 60 ~ 600 -cm ex) Ni0.2Cr0.8 , t= 900 Å : 180 -cm, Rㅁ=20 / (up to 40 / - industry standard) - (가열) electron beam evaporation TaN : 280 -cm (좀 더 정확한 저항 값 구현) - nitrogen 분위기에서 Ta 증착 (reactive sputtering) semiconductor resistor (bias resistor) I N -GaAs S.I. GaAs Linear 영역에서만 사용 V Rㅁ:  10 ~20% (부정확) ~500/ㅁ (large) E < 3kV/cm 가 되도록 저항 길이 L을 결정

Applications of Lumped Inductor ( I ) Power Amplifier Application ( I ) Conventional Amplifier Bandwidth Enhanced Amplifier Shunt peaking Bandwidth ↑ 인덕터 적용예(회로도 중심) 인덕터의 필요성, 기능(교수님 주신 논문) 서울대에서 했던 부분 첨가 동향 ( Ref : S. S. Mohan, et al., IEEE J. Solid- State Circuits, March 2000, p. 346~355)

Applications of Lumped Inductor ( II ) Power Amplifier Application ( II ) Bandwidth Enhanced Amplifier with shunt inductor L↑ L↑ ( Ref : S. S. Mohan, et al., IEEE J. Solid- State Circuits, March 2000, p. 346~355)

Applications of Lumped Inductor ( III ) Voltage Controlled Oscillator (5GHz) Q of inductor ↑ Phase Noise ↓ ( Ref : J. N. Burghartz, et al., IEEE J. Solid- State Circuits, Dec. 1998, p. 2028~2034)

Applications of Lumped Inductor ( IV ) Band Pass Filter (5.4GHz) Q of inductor ↑ Q of BPF ↑, Insertion loss ↓ ( Ref : J. N. Burghartz, et al., IEEE J. Solid- State Circuits, Dec. 1998, p. 2028~2034)

Microwave Passive Elements – Inductor (1) Wire-bonding Air-bridge to prevent metal shortage < spiral inductor > advanced inductor 구조 - Ferrite core를 사용하면 L 증가 (수백 MHz 에서는 Ferrite core 성질 잃음.) microwave 응용으로 Ferrite가 없는 air-gap inductor 사용 * spiral 에 비해 high L, small C * MEMS process로 제작 가능 (yield, cost problem) substrate gap for small C C

Microwave Passive Elements – Inductor (2) inductance 계산 Self-inductance (L,w: cm) Mutual-inductance w , s   L  s w 길이 L 6 m 10 m 2 m <MEMS process> 2.5 m <다층금속공정> - Si 공정 - advanced processes s w t w가 작으면 loss  (t를 증가시켜 loss 감소 가능) Industry standard : t=3m , Au s/w=5 m /5 m, 10 m /10 m

Microwave Passive Elements – Inductor (3) inductor for Si RF-IC spiral metal track conductive substrate로 인해 Csub  typical substrate   20 -cm (conductive) Csub Cground Si substrate Solutions (i) highly resistive substrate  ~ 104 -cm  availability , cost problem. (ii) inductor metal track 과 substrate 사이에 절연체 삽입  Csub 

Microwave Passive Elements – Inductor (4) 절연체 SiO2 r ~ 4 polyimide r ~ 3.4 BCB r ~ 2.6 절연체 (Csub 감소) Si substrate substrate <다층 금속공정 응용> inductor의 layout 효과 - Si RF IC에서는 inductor의 구현이 동작 주파수를 제한. large inductance (길이 길어짐) large fresonant & Q 각 turn의 metal폭과 gap,core의 면적의 optimization에 의해 inductor의 Q값 최대화 – 실험 및 전자장 simulation

Microwave Passive Elements – Capacitor (1) 절연체 <MIM capacitor> - 작은 series 저항 Si DRAM에서 절연체 기술의 발전 : r   면적 줄임 (higher capacitance) SiO2 : r  4 Ta2O5 : r =20~25 Al2O3 : r =10 HfO2, ZrO2 : r ~ 25 (Ba0.5Sr0.5)TiO3 : r > 300 (현재) (future) * Ta2O5 : tan = 0.02, unstable with bottom electrode * (Ba0.5Sr0.5)TiO3 - sputtering /annealing (550C~800 C) 공정 사용 - 고온 열처리로 GaAs에서는 사용 못함 (thermal damage) - unstable with bottom electrode : difficult to control stoichiometry

Microwave Passive Elements – Capacitor (2) MIM capacitor U V M2 Rt Lt C G Cfringe Lb Rb M1 bottom metal M1 w1 M2 L1 ( air bridge

Microwave Passive Elements – Capacitor (3) QMIM - bottom metal에 의해 결정 Bottom metal - smooth surface를 위해 evaporation (0.5 ~ 0.8m Au) Top metal - electroplating (~3 m Au) QMIM f (3pF capacitor) ~100 ~50 ~10GHz 1/QMIM = 1/Qconductor + 1/Qdielectric CMIM   QMIM , fresonant  CMIM 최대값 – 동작 주파수와 chip size에 의해 제한, 20pF 이하 (MMIC) CMIM Csub substrate GND • • • Csub 에 의해 signal loss 발생  fresonant  CMIM Csub

Microwave Passive Elements – Capacitor (4) MIM capacitor layout -- metal 폭의 변화에 의한 discontinuity 효과를 감소시켜주는 layout (정사각형  직사각형) ( M2 M1 ( Interdigital capacitor (0.05~1pF) Metal 두께 ~ 3 m 동일 metal로 형성 Precision capacitance Unit area capacitance ~0.3% of unit area capacitance of MIM

Substrate Integrated Waveguide ( I ) ( Ref : D. Deslandes and K. Wu, IEEE Trans. MTT, Feb. 2003, p. 593-596)

Substrate Integrated Waveguide ( II ) ( Ref : B. Liu, et al., IEEE MWCL, Jan. 2007, p. 22-24)