SPIE'031 Evaluation of Micromachined Relays for Space Applications Alexander Teverovsky, QSS/Goddard Operations Ashok K. Sharma/NASA-GSFC

SPIE'032 Benefits of micromachined switches for space applications  Low size, weight, and power consumption.  Low leakage currents and time responses.  High radiation hardness.  Integration with microcircuit technology.  High frequency performance.  Potentially high reproducibility, reliability and low cost.

SPIE'033 Purpose and Outline Purpose : evaluation of the design, electrical characteristics, and reliability of commercial DRL-CIS002 microrelays manufactured by Cronos (A JDS Uniphase Company). Outline:  Parts design and operation;  Electrical characteristics;  Mechanical shock testing;  Life testing;  Vacuum testing;  Conclusion.

SPIE'034 Parts design and operation The actuator beams are tilted at  ~0.01 rad

SPIE'035 Close-up of part’s elements The part is manufactured using three major MEMS processes: Bulk micromachining, Surface micromachining, LIGA. Nickel plated with gold

SPIE'036 Gold plated contacts Open contacts. The gap ~5  m. Close contacts forming apparently large contact area. Hard gold plating

SPIE'037 Close up of intimate contact area Contacts are formed in local areas. Rc = 1.05  0.63 Ohm (2000); Rc =  0.15 Ohm (2001) Top angle view Bottom angle view

SPIE'038 Actuation mechanism At temperature increase:  L = L  (  Ni -  Si )  T Beam elongation:  S   L/  At L = 0.7 mm,  b = 0.01, and  S  10  m, calculations yield  T = 13.6 o C At  b  -  s  S  (3-5)  L/   T  70 o C to 90 o C Actuator Beam

SPIE'039 Temperature of the actuator Maximum registered temperature vs. VH Thermal video system analysis AVIO

SPIE'0310 Effect of VH on characteristics of the part Time to close versus the heating voltage. Average Rc and IH variation with the heating voltage. Unstable operation at VH < 4.5V. At VH > 5 V Rc and  1 decreases ~10% and ~40%.

SPIE'0311 Kinetics of heating currents Heating currents at different heating voltages Two characteristic times:  ~10 to 20 ms (heating of the actuator).  ~20 to 40 seconds (heating of the surrounding bulk silicon structure).

SPIE'0312 Effect of temperature on characteristics of the microrelays IH decrease is due to resistance variations; Rc increases with T from –20 o C to +180 o C Factors affecting  and Rc: Gap variations (  b   s ) Decrease in P heater. Ductility variations. The parts can operate from -50 o C to 140 o C

SPIE'0313 Mechanical shocks in Z-direction 10 shocks at < 1000GNumber of shocks at 1000G  2 intermittent failures after 10 shocks of 1000G.  1 catastrophic failure after 10,000 shocks of 1,000G.  Three parts had normal characteristics after 10,000 shocks of 1000G.

SPIE'0314 Mechanical shocks failure Cracking of polysilicon tether Cracking of polysilicon heater

SPIE'0315 Step test results Test conditions : Vc from 0 to 70V in 10V increments, I load = 2 mA, 100 pulses, 10Hz. Result: intermittent failures start at V and I  10 mA

SPIE'0316 Life test. No load conditions. Change after ~10 5 cycles possibly due to plastic deformation of the spring and/or actuator beams. No hard failures were observed up to 6  10 7 cycles.

SPIE'0317 Life test. Hot switching. Median number of cycles-to- failure at different contact voltages and load currents.  All failures occurred after less than 10 6 cycles.  Failures during 30 V to 60 V testing were caused by stacked close contacts.  Failures at V < 30 V were mostly due to unstable, intermittent contact switching.

SPIE'0318 Life test failures Typical damage to the contacts during life testing. This failed sample stuck closed after 10 4 cycles at 60 V and 10 mA load.  Life test failures were due to microwelding at the contacts’ edges.  The intimate contacts occur only at local sites.

SPIE'0319 Examples of life test failures 60 V/5 mA 10 V/200 mA 30 V/50 mA

SPIE'0320 Vacuum test results Test conditions: Vacuum ~0.1 torr. Measurements before and after lid puncture at 4, 5, and 6 V in air and at 3, 4, 4.5, and 5 V in vacuum. Results:  Changes in the kinetics.  Lower IH.

SPIE'0321 Vacuum test failure Fracture in the polysilicon microheater Cause of failure: overheating of the microheater due to poor heat dissipation in vacuum.

SPIE'0322 Conclusion  The part can operate over a wide range of temperatures from –50 o C to +140 o C.  No failures during mechanical shock testing up to 400 G. Three out of five parts withstood 10,000 sh. of 1000 G.  The actuation mechanism and contacts can endure up to 10 8 cycles (low load conditions).  Hot switching failures: <10 6 cycles at 10 V and Ic  100 mA. N ~10 4 cycles at Vc = 60 V and Ic from 5 to 10 mA.  Hot life testing failures were caused by micro-welding at the edges of the contact surfaces.  Contact plating should be improved to provide lower Rc and reduce failures.  Parts failed in vacuum due to overheating of the polysilicon microheater.