MEMS Innovations in Semiconductor Testing
In the semiconductor industry, precision testing is key to ensuring proper functionality and quality. Two types of testing are traditionally performed:
1) wafer testing
2) chip set testing
Both types of tests require the use of relays with fast switching speed to carry various types of signals. Test boards are designed with as few as two relays or as many as several thousand per board.
Historically, reed relays or low signal mechanical relays were used in these design applications to handle the high speed switching, however, these create issues for semiconductor companies. Traditional mechanical relays have a short electrical life, causing the relay to fail within a few hundred thousand operations. When a single relay fails, the entire tester will need to be shut down. This can significantly influence the total cost of test through debugging, rework, and loss of semiconductor throughput.
Today’s consumer market is demanding faster download speeds, transfer rates, and improved graphics. The semiconductor industry addresses these demands by developing chips that operate with increased data rates. For example, the current generation of PCI Express (PCIe 3.0) operates at data rates of 8GT/s. The next generation (PCIe 4.0) is targeted to have data rates of 16GT/s. For this next generation of PCI Express, there are currently no mechanical relays on the market that can operate at these switching speeds.
Additionally, mechanical relays have a large footprint. This can cause issues as increased channel counts require more relays on a single board. Large mechanical relays consume significant board space and limit the number of channels that can be tested at a time.
Leveraging a particular type of MEMS technology can create a relay that can overcome these obstacles. What is MEMS? MEMS is short for Micro Electro Mechanical Systems. It is the technology of very small devices that are fabricated by semiconductor device fabrication technologies. Some micro-scale mechanical components, sensors, actuators or electrical circuits are integrated on one silicon substrate, glass substrate, organic substrate, and so on.
Taking into consideration the targeted data rates of PCIe 4.0 with the development of a new Double-Pole Double-Throw (DPDT) MEMS relay (Omron) that will meet and exceed the semiconductor test industry’s requirements. This new relay can achieve performance levels that rival traditional relay ratings. These include, but are not limited to:
-Insertion loss of 2.0dB at 20GHz (differential)
-Isolation of 25dB at 20GHz (differential)
-Return loss of 10dB at 20GHz (differential)
-Hot switch rating of 1.0VDC at 1mA resistive
The DPDT MEMS relay is guaranteed to operate for a minimum of 100 million cycles, and they have test data showing relays exceeding 750 million cycles. This lifetime far exceeds those of traditional relays used for semiconductor testing. This can offer many benefits for semiconductor testing, the most notable being a reduction in total cost of test.
The DPDT MEMS relay offers high performance and long life, and also comes in a compact package (6.0 x 6.0 x 2.5mm). This gives the relay an extremely small footprint, allowing the test engineer to increase channel count and/or test sites.
The small footprint is a result of a unique design and construction of the relay. The MEMS relay consists of three layers which are Glass-Silicon-Glass. The top glass layer is used for protecting the actuator and is fabricated using Thru-Glass-Via(TGV) technology. Advancements in TGV offer improved RF characteristics by allowing greater bandwidth. The middle layer consists of movable electrodes made from Silicon. These silicon actuators help improve the lifetime of their relays as Silicon does not suffer from switching fatigue unlike metal actuators. The bottom glass layer contains the signal lines and fixed contacts and electrodes. The entire assembly is then hermetically sealed and backfilled with a gas which further aids to the life of the relay.
Applying a voltage between the fixed and moveable electrode will generate an electrostatic force. This will then pull in the moveable electrode causing the relay to actuate. When the driving voltage is turned OFF, the electrostatic force will disappear and the actuator will go back to its original position. The signal line and the moveable contact consist of pure metal wiring and serve as a mechanical switch which can handle DC to High Frequency Signals.
This DPDT MEMS relay has taken drive circuit control to the next level by integrating a DC-to-DC converter. This allows the designer to control the relay with a standard 5.0VDC eliminating the need for an external charge pump circuit.
Demand for increased bandwidth continues to grow as more and more consumers want increased speeds and improved graphics. This puts significant strain on semiconductor companies to quickly advance semiconductor technology. Omron’s innovative DPDT MEMS relay is able to alleviate this strain by providing a compact product with unparalleled performance and life, thus lowering the overall cost of test while improving time to market.