Reliability of Dielectric Less RF-MEMS Capacitive Switches

Transcription

1 Reliability of Dielectric Less RF-MEMS Capacitive Switches David Mardivirin, Pierre Chauveau, Arnaud Pothier, Aurelian Crunteanu, Pierre Blondy XLIM, CNRS, Université de Limoges Limoges, F-87000, France (all french website )

2 What are RF-MEMS? Purpose: Use mechanics to achieve electrical function: high potential to introduce tunability or intelligence in RF sub-systems Switch and varactors Interests: Very high performance components (low loss, high isolation) Very linear components Low power consumption and low power dissipation Reliability potentially high vs conventionnal relays (10 Billion cycles vs 10 Million ) Roadblocks: Reliability not fully demonstrated Packaging is still challenging Cost will certainly be higher that expected at least in the beginning.

3 State of the art capacitive switches 100 Billion cycles reported

4 Conventionnal MEMS capacitive Switches Conventionnal Capacitive MEMS switches Metal membrane Dielectric Up State Down State

5 Reliability Charge injection + trapping V 20 Volts over 0,2 µm Charge trapping is the main failure mode for RF-MEMS capacitive switches

6 Charge injection and trapping Injection inside the dielectric layer k C v εr V

7 Charge injection and trapping Injection inside the dielectric layer k C v εr V1 V

8 Charge injection and trapping Injection inside the dielectric layer k C v εr V1 V

9 Charge injection and trapping Injection inside the dielectric layer k C v εr V1 V

10 Charge injection and trapping Injection inside the dielectric layer k C v εr V1 V Switch failure!

11 So What? Reduce sensitivity to Q Reduce Q more C / surface area Advantages: -much less sensitive to charges - faster - integrated drawbacks: - Lower contrast Advantages: - Much less sensitive to charges - Simple drawbacks: - Less contrast

12 Air dielectric switches Air dielectric switches Dielectric Air Avantages: No charge trapping, no complicated actuation waveform Drawbacks: Larger structures Lower On/off

13 Proposed structure How to improve contrast?? Higher tip = low up state capacitance Gap~0,5 µm Up State Moderate height = moderate pull in voltage Down state Overall, the contrast is higher than for conventional structures, and voltages remain the same

14 Capacitive Dielectric Less Switches

15 Projet multipartenaires SMARTIS : Smart Thin Films on Alumina Substrate Objectifs: Améliorer la fiabilité et la durée de vie du composant sans dégrader ses performances par La suppression de la couche diélectrique de l actionneur électrostatique L introduction de matériaux spécifiques au niveau des contacts Measurement planes Butée métallique introduite en remplacement du film mince isolant Nouvelle génération de micro commutateur dit «sans diélectrique»

16 Residual Charging Air Sapphire substrate Cantilever Actuation electrode (60V) Sapphire substrate High electric field magnitude area

17 Test Bench Vacuum probe station

18 Applied unipolar voltage waveforms Test Signals > 97.7% time down state charging C(V) testing < 2.3% down state discharging 15ms 985ms Time variable duty cycle

19 Typical Results

20 Typical Results dv = A.t n 97.7% 75% 50% 25% Identical Curves

21 Examples with various duty cycles Pull down voltage shift (V) % 50 % 25 % Time (s)

22 Future Works: Mechanical Assessment

23 Conclusions Dielectric less actuators greatly improve the reliability of capacitive switches They are different from conventionnal capacitive switches Duty cycle has been identified as the main accelerating mechanism 90% in the down state = a few month lifetime 50% in the down state= a few tens of month Bipolar: lifetime >> 10 years in all cases. Charging is probably not the main issue. Mechanical stress, number of cycles will be an increasing subject for RF-MEMS reliability in the next years.

24 Acknowledgements Charging studies are supported by MoD (DGA) Mechanical models are supported by Astrium Launch Vehicles, (Saint Médard en Jalles)