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Electropages — April 9, 2025
Featuring Chris Keimel, Menlo Micro CTO
For more than 150 years, electromechanical relays (EMRs) have served as the workhorse of electrical switching, bringing society into an electrified world by connecting, controlling and protecting our powered devices and infrastructure.
With electrical machinery operating in the order of seconds, there was never a need to make switches faster, just smaller and operate longer.
As society advanced from a mechanised age driven by motors into an information age driven by data and its processing through chip-based devices, the need for speed began to take shape, first through our devices and more recently within our connected infrastructure through increased automation and smart electrical systems.
EMRs were never designed to meet the speed challenge. They were designed with simple criteria in mind, to be low-loss when on and isolated when open.
EMRs rely on moving parts to change states; however, these moving parts wear with every operation, degrade with every arc event and become less reliable over time. In an era where energy efficiency is paramount, EMRs have another drawback besides speed; many require a few hundred milliwatts to a few watts of power to drive a coil that operates and keeps the contacts closed.
This constant energy demand not only wastes power but also reduces the overall efficiency of the circuit.
Electromechanical relays are not the only way to control the flow of current; semiconductors are also used. While the first semiconductor devices were designed for signal amplification, it was not until the invention of the Integrated Gate Bipolar Transistor (IGBT) in the late 1970s that solid-state devices began to be widely adopted for high-speed control of electrical power.
These devices, manufactured using semiconductor materials, aimed to address some of the limitations of EMRs, such as slow actuation speed, high noise levels and limited lifespan, were not designed to meet the full spectrum of performance demands within today's modern systems.
Consequently, these semiconductor-based switches have only been adopted in niche applications where millisecond and faster speeds are required, and millions and billions of operations are necessary because they trade off and lack the core capability of EMRs (low loss and isolation).
Solid-state switches are used in harsh environments, where shock and vibration are present, where service and replacement are challenges, and where high operational counts are paramount.
Solid-state switches introduce additional drawbacks that often add complexity to electrical systems. They do not fully isolate circuits as they have no air gap; they require additional thermal management as they are semiconducting and not fully metallic, and their body diode effect limits conduction in a single direction.
These limitations result in bulkier designs that detract from the chip-based miniaturisation of the switch, making them less desirable. Moreover, a semiconductor-based switch does nothing to solve the fundamental efficiency problems of electromagnetic relays; it is a more lossy solution because of both its semiconducting materials and the constant power required to drive the gates to activate the device.
From Electromechanical to Solid-State: Strengths and Limits
Recently, a completely new method of switching, based on microelectromechanical systems (MEMS), has emerged. MEMS technology is nothing new; these devices are around us performing everyday tasks without us realising their existence.
They control your car's airbag deployment, sense tire pressure, and are the microphones in your handheld devices. They filter spurious communication signals and provide chip-based inertial stabilisation for autonomous platforms.
More recently, they are being used as miniature ohmic electrical switches deployed in wireless infrastructure and satellite communications links, and they are used to reconfigure advanced electrical test systems for some of today's most advanced CPU and GPU chips. (Update begins) In the mid-2000s, GE began its development of metal MEMS switch technology to bring microsecond switching speed to a truly low-loss ohmic switch in a chip-scale solution.
