New Circuit Breaker Technology Impresses US Navy

­Switching is traditionally accomplished by electromechanical devices that tend to degrade over time because of wear. They are also relatively slow to act, are bulky and can be difficult for automated assembly to handle. More recently, solid-state switches and relays have been developed for the task. These solutions get rid of many of the drawbacks of electromechanical devices, being quicker and smaller, but they have their own drawbacks. Semiconductors require a voltage drop to operate, and in an application like a relay where the circuit is on constantly, that drop can cause a drop in efficiency over time. The inefficiency also generates heat, which has to be disposed of, normally by a heat sink, adding volume and cost to the final solution. 

Now, Menlo Micro has developed a different type of switching device that the company claims offers outstanding performance with no real drawback. It uses a type of MEMs technology with circuits built from conductors and insulators rather than semiconductor material. The unit cell design is very simple, consisting of two contacts embedded in insulating glass, with a beam that connects the two when a small electrostatic charge is applied. The unit cell measures only 50μm x 50μm, and hundreds of these cells can be combined together in series or parallel in a single die. For example, in one solution, Menlo uses 400 unit cells in a device that can easily switch 10A. Additional devices can easily be added for further scalability.

At PCIM I had the chance to talk to Menlo’s CEO, Russ Garcia about the company’s Ideal Switch. He says the process to make the switch is not complex, “it is simply conductor in glass. We can put pins very close together because the breakdown voltage of glass insulator is very high. This is a probably the simplest semiconductor manufacturing process that I've ever been involved with and it is very scalable. We fabricate on fused silica glass, so our starting material cost is lower than silicon on insulator, the process uses normal semiconductor manufacturing equipment and involves only 15 masking steps, with no specialized lithography”.

The results give a device that has almost no resistance while on and almost infinite resistance when off. Initially, Ideal Switch was targetted at RF applications because of its linearity and low insertion losses. The company then realized the potential of the device in certain power applications.

Garcia explained, “the devices are uniquely suited for circuit breakers and other applications that are are ‘normally on’, for example in power distribution and control. In these applications, conductivity is the most important parameter, you don't need the speed of a semiconductor. The thermal over-design that's required for silicon carbide solutions is not required in our in our case, and that lowers cost, size and weight”.

The technology looks very interesting and Menlo have won a contract to develop the technology further from the U.S. Navy for advanced circuit breakers.