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RF MEMS Switch Reliability - Are We There Yet?

Tue, 09/27/2011 - 12:58pm

DonnaSandfoxby Donna Sandfox, Product Manager, Omron Electronic Components LLC

U
sing MEMS devices for RF signal switching has been a long time coming.  The R&D efforts to bring this technology to a viable commercial product have taken longer than it took from President Kennedy’s congressional address in 1961 which kicked the Apollo program into high gear to the landing of a man on the moon in 1969.  There have been many starts and stops, and VC companies have come and gone, understandably making some hesitant to embrace the technology.  So the question begs…  ARE WE THERE YET?

WE HAVE LANDED, and those first steps have been with taken with extreme care.  The release of Omron’s RF MEMS switch was the culmination of several years of research and development, drawing on their long expertise in electromechanical relays and MEMS processes, including metallurgy development for a proprietary alloy.  Not willing to put their reputation for high quality electromechanical components in jeopardy, Omron put their RF MEMS switch through a strict battery of quality and reliability testing prior to releasing a product to the market.  That, however, turned out to be just the beginning of the journey.  

To Omron’s dismay, when the product (p/n 2SMES-01) was released in the fall of 2008, the market didn’t immediately race to this product that had been so eagerly anticipated.  The market’s opinion of “MEMS RF Switches” had already been tainted.  The initial target market for the product was, and continues to be, Automatic Test Equipment.  The semiconductor test board designers liked what they saw on paper, but needed time to run the product through its paces.  Over the last 3 years much additional testing has been conducted both by Omron and its customers, covering a wide range of operating parameters. 

The 2SMES-01 (see Figure 1) relay consists of two MEMS single pole, single throw chips; independently actuated, they can be used for SPDT switching of broad bandwidth of signals from DC to over 12 GHz.  

OmronFigure1

Figure 1, Omron’s 2SMES RF MEMS Switch

Due to the fact that a physical contact is made, the product maintains the high frequency characteristics found in electromechanical relays.  The MEMS static drive mechanism (no coil) contributes to a life expectancy usually associated with solid state devices.  Additionally, the product’s small size, fast response time, low power consumption and low leakage (see Table 1) combine to make it a very attractive option.

Size 

5.2 x 3.0 x 1.8 mm LGA 12 package

Input Voltage 

34 VDC +/- 5% 

Power Consumption 

10 µW (max) 

Operate/Release Time 

100 µsec (max) 

Leakage Current 

<100 fA @ 100V 

Initial Contact Resistance 

1.0 W (typical) 

Rated Load 

0.5 mA at 0.5 VDC Resistive Load 

Max Switching Voltage 

0.5 VDC 

Max Switching Current 

0.5 mA 

Max Carry Voltage 

10 V 

Max Carry Current 

100 mA 

Max Carry Power 

CW: +30 dBm at 2 GHz 

 Max Peak Power 

CW: +36 dBm at 2 GHz 

Characteristic Impedance 

50 W

Insertion Loss 

0.2 dB at 1 GHz 

Isolation 

30 dB at 15 GHz 

Return Loss 

10 dB at 10 GHz 

-3dB Roll-off Frequency 

> 12 GHz 

Life Expectancy 

100 Million Cycles (min) 0.5V/0.5mA resistive load  

Hot Switching Life 

> 50 Million Cycles (MCBF) 1V/10mA, 10V/1mA

Table 1: Ratings/Characteristics 

For high speed digital semiconductor applications such as PCIE 3.0 and USB 3.0 loop-back testing, board space is often at a premium, so small package size is an important factor.  Even more essential are good high frequency characteristics and a long life expectancy, as board repairs are quite costly. 

To ensure RF MEMS relays were up to the demands of this industry, both Omron and their customers put the 2SMES-01 through several successions of tests at application-specific conditions, pushing some characteristics well beyond their ratings.  See Figure 2 for B10-life data at extended switching loads.  It should be noted that a failure was defined as change in contact resistance greater than 1 Ohm (not an operational stoppage).

OmronFigure2

Figure 2:  2SMES-01 B10-life vs. Switching Load

During the RF Hot Switching test shown in Figure 3, the contacts were continuously monitored for sticking and no-contact errors to ensure proper operation.  No errors were detected through the 100 million cycle test.  Note the stability of the insertion loss and isolation over the duration of the test.

OmronFigure3

Figure 3:  2SMES-01 HF Characteristics under RF Hot Switching with an input power of +20 dBm @ 2 GHz

Additional applications for RF MEMS Switches include RF instrumentation and accessories such as filter banks, step attenuators and RF switching boxes, as well as high speed telecommunication equipment.

In all applications using a MEMS RF relay with static drive technology, ESD (Electrostatic Discharge) is of concern.  Customers need to ensure that their assembly process (or 3rd party board house) is equipped to handle the sensitive parts, and that employees are properly trained in grounding techniques.  An audit from an independent ESD specialists can be a very worth while exercise, saving much time and expense in the long run.  Furthermore, the placement of the switch within the equipment should be considered in the design process to avoid areas prone to static shock from user interface or other sources.

Launching an RF MEMS Switches into the market has been a long and arduous process, however, the resulting confidence in the product’s capabilities has been enhanced with each step.  Building on this success, Omron is moving forward to expand the product line.  Currently in development is a low cost RF MEMS Switch for mobile devices, and a 20 GHz Double Pole Double Throw switch for the ATE market.

So, back to the question at-hand, are we there yet?   We are!  And the exploration and expansion continues.

www.omron.com


Posted by Janine E. Mooney, Associate Editor

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