In the following presentation, we highlight field-proven, relevant test solutions based on a cryogenic wafer-probe station. Special attention is given to overcoming the calibration standards instability, contact repeatability and reliability issues caused by the extreme environmental conditions. We will present the solution that enabled characterizing of RF MEMS devices at cryogenic condition with the benchmarking level of measurement accuracy and confidence.

1. 16th IEEE European Test Symposium
May 23-27, 2011
Wafer-Level RF MEMS Devices
Characterization in Cryogenic
Environment
Gavin Fisher, Andrej Rumiantsev,
Frank-Michael Werner, Stojan Kanev

2. Outline
 RF MEMS Test Challenges
 System Solution for RF MEMS
 Measurement Examples
 Conclusion

3. RF MEMS Test Challenges
 MEMS device: microsystem based planar fabrication technology
combining mechanical and electrical functions (multi-physics
interaction)
 Testing and characterization are extremely sensitive to ambient
parameters
 Tests require:
– Controlled (closed) environment
– RF and microwave interface
 For RF testing thermal stability of probes and cables is
essential to maintain calibration stability
– Core solution, Keep probes and cables at DUT temperature
– Calibration monitoring to provide accurate feedback of
calibration state

4. RF MEMS Test Challenges (cont.)
 Probing of whole wafer, wafer pieces and dies
 Maintenance of calibration substrates
 Contact reliability
 Contact repeatability
 Electrical performance of RF probes
 Temperature stability of calibration standards
 Integration with various test instrumentation

5. Outline
 RF MEMS Test Challenges
 System Solution for RF MEMS
 Measurement Examples
 Conclusion

6. Putting a Prober Inside a Vacuum Chamber
Reserve 4x RF Feedthrough
67 GHz
Reserve for
Reserve PH #8
for PH #9 DC Triax
Fixed cold shield
4x DC Triax
Feedthrough
PH #6 PH #3
67GHz DC Triax
PH #5 PH #2
67GHz 67GHz
PH #4 PH #1
DC Triax 67GHz
Removable
cold shield
PH #7 Reserve
DC Triax for PH #10
Venting Valve
Y X
Z
Chuck Stage
Control

7. Putting a Prober Inside a Vacuum Chamber
Enables:
Temperature
Vacuum
Gases composition
Applications:
High pressure RF MEMS
Light and sound Emerging MEMS
shielding Micro fuel cells
Microbolometers
EMC
Gyroscopes
Humidity Accelerometers
Pressure sensors

8. Cryogenic System for Device Characterization
 Temperature range: 4K … 675K
 Up to 8 positioners
 Low signal IV/CV: <100fA
 High frequency: up to 67GHz
 Integration kits for Agilent and
Keithley
 EM shielding and light tightness

9. Motion Monitoring in Cryogenic Environment
 Integration with Polytec MSA-500 Micro System
Analyzer
Example of RF MEMS Switch

10. Features – Wafer, Sample and Die Carriers
Carrier solution for Manual Systems
prepared for fixing RF calibration
substrates
Special carrier solution for Special carrier solution for diced
Standard 200 mm wafer carrier fixing multiple single substrates pieces with various shapes

11. Features – Vacuum Positioners
 Easy and reliable probe landing
 Short and stiff arms
 Manipulation from outside by rotary
feedthroughs
 Magnetic foot (standard) for highest
flexibility in probe configuration
 12 mm XYZ movement range
 Arms:
– DC triaxial flex
– DC for AP&T
– RF for IZI Probe etc.
– DC&RF for
Multi IZI Probes

12. Features – Vacuum Positioners
 DC probes (triax, coax)
 AP&T probe for CV
 RF Probe up to 67GHz
 Multi IZI Probes
 Cryogenic probe arms with
active probe and cable cooling
to ensure stable
measurements
 High vacuum feedthroughs
 Calibration substrates

13. Outline
 RF MEMS Test Challenges
 System Solution for RF MEMS
 Measurement Examples
 Conclusion

14. System Features: System Drift, 4 Hours
|Sij' - Sij|/|Sij| and |Sii' - Sii|
0.15
System Drift, 4K
System Drift, RT
0.10
0.05
0
0 10 20 30 40
Frequency (GHz)
System drift @ 4K is comparable with the room temperature
H. Geissler, A. Rumiantsev, S. Schott, P. Sakalas, and M. Schroter, "A novel probe station for helium temperature on-wafer
measurements " in ARFTG Microwave Measurements Conference-Fall, 68th, 2006, pp. 67-73.

15. Wincal XE – Cal monitoring alarms
 Wincal can perform a spot measurement and
provide alarm if system has drifted beyond limits

16. Measurement aid – Wincal XE
 Probing at cryogenic temperatures can be challenging and it is helpful
to be able to check that good contact is established
 Wincal XE can do this with a single button press

17. Wincal XE Advanced reporting
 Wincal can perform pad parasitic removal de-
embedding and parameter extraction“on the fly”

18. Temperature Stability of Standards
Line (Thru) Load
Temperature stable wafer-level calibration standards for
accurate measurements down to 4K
A. Rumiantsev, R. Doerner, and P. Sakalas, "Verification of wafer-level calibration accuracy at cryogenic temperatures " in
ARFTG Microwave Measurements Conference-Fall, 68th, 2006, pp. 134-140.

19. Cryogenic |Z| Probe Contact Repeatability @ 4K
First Contact Second Contact
0 DB(|S[1,1]|) 0
Thru DB(|S[1,1]|)
-10 -10
Thru_2
-20 DB(|S[2,2]|) -20
Thru DB(|S[2,2]|)
-30 -30 Thru_2
-40 -40
-50 -50
-60 -60
-70 -70
-80 -80
-90 -90
-100 -100
0 10 20 30 40 50 0.04 10.04 20.04 30.04 40.04 50
Frequency (GHz) FREQUENCY (GHz)
Excellent contact repeatability guarantees reliable and
trustable results
*Measured with thru standard

20. RF MEMS Switch
 Procedure:
– S parameters measurement before
cycling
– C(V) measurement
– Cycling @ 100 Hz, unipolar, 55V, 50%
duty cycle
– S-parameters after cycling
 To do and outcome :
– Extraction of ∆V vs. cycles
– Pull-in Pull-out parameters dependence
on the environment conditions

21. CV Curves for Different Testing Conditions
1 .2
1
(1 ) 2
1 .0
(2 ) 3
10
(3) 4
(4) 0.8
C (p F )
0.6
∆V (V)
0.4
1
0.2
0.0
10 1 00 1 000 -80 -60 -40 -2 0 0 20 40 60 80
N b o f c yc le s Vo ltag e (V)
1: Room ambient @ ~296°C, 45% RH
2: Vacuum @ 1.4E-5 mbar – 296K
3: N2 @ 1.02 atm – 296K
4: Vacuum @ 2.2E-6 mbar – 223K

22. S-Parameters for Different Testing Conditions
B E F O R E C YC L IN G B E F O R E C YC L IN G
0
0.0
Before cycling
-0.5
-2 0
-1 .0
S 1 1 (d B )
S 2 1 (d B )
-1 .5
-40 (1 ) (1 )
(2 ) (2 )
-2 .0
(3) (3)
-60 (4) (4)
-2 .5
0 10 20 30 40 50 60 -3.0
0 10 20 30 40 50 60
GHz
GHz
0.0
0
After 1000 cycles
-0.5
-2 0
-1 .0
S 2 1 (d B )
S 1 1 (d B )
(1 )
-1 .5
-40 (1 ) (2 )
(2 ) (3)
-2 .0 (4)
(3)
(4)
-60
-2 .5
0 10 20 30 40 50 60 0 10 20 30 40 50 60
GHz GHz

23. Outline
 RF MEMS Test Challenges
 System Solution for RF MEMS
 Measurement Examples
 Conclusion

24. Conclusion
 Wafer-level testing of RF MEMS significantly reduces
fabrication cost and time to market
 Cryogenic Probe Systems covering the whole range
of RF MEMS test requirements are available
 System design and measurement know-how of
Cascade Microtech provides you with “environment
independent” measurement accuracy, repeatability
and confidence in your results

25. Acknowledgement
Jason Ruan, Alexandre Rumeau,
Laurent Bary and Fabio Coccetti
from CNRS, LAAS, Toulouse (France)
for excellent support with the
measurement results
of the RF Switches

26. Questions?
If you have any questions or comments, please
contact:
Frank-Michael Werner
Business Manager
VAC / CRYO Systems and MEMS Test
E-mail: frank-michael.werner@cmicro.com
Office: +49 (35240) 73-330
Mobile: +49 151 1210 8668