1. New Low Cost & High Performance Transmission Line
Eun Sub Shim
Micro/Nano Systems & Controls Lab.
SNU

2. Contents Introduction Survey New Design Conclusion References
HRS t-lines
LRS t-lines
Best Performances
New Design
Design Consideration
Wet-etched CPW
Structure
Process
Properties
Conclusion
References

3. Michigan Microstrip (1993-1998)
HRS
Michigan Microstrip ( )
[1]
SMM
(shielded membrane microstrip)
Advantage
No dielectric loss
Self-packaging
Loss: < 0.6 ~110 GHz
HRS
SiO2/Si3N4/SiO2, 1.5 µm
Metal: Ti/Au, 1.2 µm
Selective etching: EDP
Bonding: conductive epoxy

4. Michigan CPW (1998-2002) HRS [2] Membrane CPW MFGC
(micromachined finite ground CPW)
Advantage
Reduce dielectric loss
Simple process
Loss: GHz
HRS
SiO2/Si3N4/SiO2, 1.5 µm
Selective etching: EDP
Metal: Cr/Au, µm

5. GEC Marconi Instrument CPW (1998)
HRS
GEC Marconi Instrument CPW (1998)
[3]
Trenched CPW
Loss: GHz
650 µm-thick Ohm-cm HRS
Metal: Al evaporation 1.46 µm
CF4 plasma etch

6. SNU CPW (2000) HRS [4] ECPW (elevated), OCPW (overay)
Loss: 1 40 GHz
Glass substrate
Metal1: Ti/Au electroplate 3 µm
Metal2: Cr/Au electroplate 3 µm
Thick PR(AZ 4620): 15 µm
PR Curing: 200oC

7. LAAS-CNRS CPW (1997, 2003) LRS [5] CPW on Membrane CPW on BCB
Loss: 1 dB for 2,4,6 40 GHz
Access port loss is dominant
20 Ohm-cm silicon (350 µm)
SiO2/Si3N4, 1.4 µm (0.8/0.6)
Metal: 2.5 µm
Silicon etch: KOH
CPW on BCB
Loss: GHz
20 Ohm/cm silicon
Deep RIE : 10 µm
BCB: 10 µm
Metal: Ti/Au, 3 µm Si
BCB
Metal

8. NIST CPW (1997) LRS [6] Circuit: foundry survice (Magic)
Glass with etch hole
0.6 µm-thick Al pattern in glass
460 µm-thick silicon
Hybrid etch process
Isotropic etch: XeF2 (16 min)
Anisotropic etch: EDP (1h 92o)
Loss: 4 40 GHz

9. KAIST air gap lines (2002) LRS [7] Ground electroplating + LIGA x 4
Ti/Cu electroplating, 12 µm
Thick Oxidized Porous Silicon (OPS)
10 Ohm-cm silicon substrate
Oxide thickness: 20 µm
Air gap CPW
Loss: GHz

10. KAIST CPW (2003) LRS [8] Thick Oxidized Silicon
Oxide thickness: 7 µm
Conductivity: 10 Ohm-cm
Ground electroplating + LIGA x 2
PR1: AZ 9260 (10 µm)
PR2: ?
Ti/Cu electroplating, 10 µm
Thick Oxidized Porous Silicon
Loss: GHz

11. SNU Thin Film Microstrip (TFMS) line
[9]
MMIC 설계에 필요한 집중소자를 BCB위에 제작하여 signal과 같은 상에 위치시키는 구조 제안
BCB 식각시 PR mask 사용
능동소자를 signal과 같은 위치에 놓기 위하여 기판을 깎아서 ground를 낮게 형성함
TFR과 capacitor를 signal과 같은 위치에 형성함
TFMS line loss
GHz

12. Cheap & simple process Best Performance HRS LRS Michigan (1993-1998)
Loss: < 0.6 ~110 GHz
Three HRS substrates
Bonding alignment
Back side process
LRS
KAIST (2003)
Loss: GHz
Complicated process
Cheap & simple process

13. ? Design Consideration Substrate coupling Leakage current path
Isolating transmission line from substrate
Field out of substrate
Leakage current path
Trench, air gap
Metal loss
Smooth metal surface, Thick metal line
Electroplating vs. Sputtering
Transition
Conventional T-line to New T-line ?
OLD
NEW

14. Wet-etched CPW
Zo=49 Ohm
Loss= GHz

15. Structure Minimize substrate coupling No leakage current path
Silicon
Metal
Minimize substrate coupling
No leakage current path
Rigid structure (thick metal)
Smooth metal surface
Simple process
10 um
100 um
100 um
71 um
54.7o
280 um

16. Process Single mask process!! Cheap & Simple Process!!
1. Photolithography
4. CMP
Silicon PR
Metal
2. KOH etch
5. TMAH etch
3. Electroplating
Single mask process!!
Cheap & Simple Process!!

17. Attenuation Attenuation 0.21 dB/cm @ 20 GHz 0.57 dB/cm @ 40 GHz

18. Attenuation KAIST CPW paper (20 GHz) KAIST CPW simulation
Fabricated: 0.35 dB/cm
Simulation: 0.22 dB/cm
KAIST CPW simulation
Loss: GHz
Wet-etched CPW simulation
GHz
GHz
Comparable to world’s best CPWs
GEC Marconi
HRS
(1998)
Michigan HRS (2002)
KAIST LRS (2003)
0.2
This work
LRS

19. Rigid structure Other CPWs Wet-etched CPW
Membrane type : Michigan, LAAS-CNRS, NIST
SiO2/Si3N4 membrane (t<1.5 µm)
Suspended metal : KAIST
Cu (t=10 µm, w=100 µm)
Wet-etched CPW
Suspended Metal bar
Cu (tmax= 71 µm, w=100 µm)

20. Simple process Single mask process No misalinement effect
Cheap process
Cf. other lines
Membrane type : Michigan, LAAS-CNRS, NIST
Minimum 2 mask is needed
Suspended metal : KAIST
Minimum 3 mask is needed

21. Conclusion CPW survey New Design: Wet-etched CPW HRS
Michigan ( )
Loss: < 0.6 ~110 GHz
LRS
KAIST (2003)
Loss: GHz
 Expensive & Complicated process
New Design: Wet-etched CPW
Low loss: GHz, 1.19 <100 GHz
Rigid structure
Single mask process
 Low cost & High performance CPW fabrication is possible!!!

22. References
[1] L. P. B. Katehi, G. M. Rebeiz, T. M. Weller, R. F. Drayton, H. Cheng and J. F. Whitaker, “Micromachined Circuits for Millimeter- and Sub-millimeter-Wave Applications”, IEEE Antennas and Propagation Magazine, Vol. 35, No. 5, Oct
[2] K. J. Herrick, T. A. Schwarz, and L. P. B. Katehi, “Si-Micromachined Coplanar Waveguides for Use in High-Frequency Circuits”, IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 6, June 1998.
[3] S. Yang, Z. Hu, N. B. Buchanan, V. F. Fusco, J. A. C. Steward, Y. Wu, B. M. Armstrong, G. A. Armstrong, and H. S. Gamble, “Characteristics of Trenched Coplanar Waveguide for High-Registivity Si MMIC Applications”, IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 5, June 1998.
[4] J. Park, C. Baek, S. Jung, H. Kim, Y. Kwon and Y. Kim, “Novel Micromachined Coplanar waveguide Transmission Lines for Application in Millimeter-Wave Circuits”, Japanese Journal of Applied Physics, Vol. 39, No. 12B, Dec
[5] F. Bouchriha, K. Grenier, D. Dubuc, P. Pons, R. Plana, and J. Graffeuil, “Minimization of Phassive Circuits Losses realized on Low Resistivity Silicon Using Micro-Machining Techniques and Thick Polymer Layers”, 2003 IEEE MTT-S Digest., 2003.
[6] V. Milanovic, M. Gaitan, E. D. Bowen, and M. E. Zaghloul, “Micromachined Microwave Transition Lines by Commercial CMOS Fabrication”, IEEE Transactions on Microwave Theory and Techniques, vol. 45, no. 5, May
[7] I. Jeong, S. Shin, J. Go, J. Lee, C. Nam, and D. Kim “High-Performance Air-Gap Transmission Lines and Inductors for Millimeter-Wave Applications”, IEEE Transactions on Microwave Theory and Techniques, vol. 50, no. 12, Dec
[8] E. Park, Y. Choi, B. Kim, J. Yoon, and E. Yoon, “A LOW LOSS TRANSMISSION LINE WITH SHIELDED GROUND”, IEEE The Sixteenth Annual International Conference on Micro Electro Mechanical Systems, 2003., Jan
[9] 송생섭, 노훈희, 서광석, “Structural improvement of Thin Film Microstrip line for MMIC applications using MCM-D”, 제 11회 한국 반도체 학술대회, Feb