A revolution between ON & OFF

Two years ago in November, Analog Devices made a major breakthrough in MEMS technology and announced the launch of a revolutionary 0Hz (DC) to GHz switch solution - ADGM1304 and ADGM1004 RF MEMS switches. For the first time, the industry provided an excellent alternative to the traditional relay method, breaking through the electromechanical relays that were adopted by the electronics industry more than 100 years ago.

In two years, MEMS switches have helped a large number of automatic test equipment (ATE) and other instruments achieve accuracy and versatility, helping customers reduce test costs and power consumption and shorten product time to market. MEMS switches are about to replace relays in industries such as aerospace and defense, healthcare, and communications infrastructure equipment.

The key to ADI's MEMS switch technology is the concept of an electrostatically actuated micromachined cantilever beam switch element. Essentially, it can be thought of as a micrometer-scale mechanical switch with metal-to-metal contacts actuated electrostatically.

The switch is connected in a three-terminal configuration. Functionally, these terminals can be thought of as the source, gate, and drain. Figure 1 is a simplified schematic of the switch, with Case A showing the switch in the off position. When a DC voltage is applied to the gate, an electrostatic downward pull is created on the switch beam. This electrostatic force is the same as the attractive force between the positive and negative charged plates of a parallel plate capacitor. When the gate voltage is ramped up to a high enough value, it creates a large enough attractive force (red arrow) to overcome the spring resistance of the switch beam, and the switch beam begins to move downward until the contact touches the drain.

Figure 1. MEMS switch operation process, A and C represent the switch off, B represents the switch on

This process is illustrated in case B in Figure 1. Therefore, the circuit between the source and drain is closed and the switch is now on. The actual amount of force required to pull down the switch beam is related to the spring constant of the cantilever beam and its resistance to motion. Note: Even in the on position, the switch beam still has a spring force pulling up the switch (blue arrow), but as long as the electrostatic force pulling down (red arrow) is greater, the switch will remain on. Finally, when the gate voltage is removed (case C in Figure 1), that is, with 0 V on the gate electrode, the electrostatic attraction disappears and the switch beam, acting as a spring, has enough restoring force (blue arrow) to break the connection between the source and drain and then return to the original off position.

A MEMS cantilever switch beam

(You can see the five contacts connected in parallel and the hinge structure with a gap underneath.)

MEMS switches require a high DC drive voltage to electrostatically actuate the switch. To make the device as easy to use as possible and further guarantee performance, Analog Devices has designed a companion driver IC to generate the high DC voltage, which is co-packaged with the MEMS switch in a QFN form factor. In addition, the generated high drive voltage is applied to the gate electrode of the switch in a controlled manner. It ramps up to a high voltage in microseconds. The ramp-up helps control the pull-down and pull-down of the switch beam, improving the actuation performance, reliability, and lifetime of the switch. The driver IC requires only a low voltage, low current power supply that is compatible with standard CMOS logic drive voltages. This co-packaged driver makes the switch very easy to use and its power consumption requirements are very low, in the range of approximately 10 mW to 20 mW.

The ADGM1304 is a broadband, single-pole, four-throw (SP4T) switch that operates down to 0 Hz/DC, making it an ideal switch solution for a variety of RF applications. Enabling smaller, more flexible, and more reliable low insertion loss switches significantly reduces size and component count, and significantly reduces cost.

With the ADGM1304 MEMS switch product, ADI developed the ADGM1004 MEMS switch to enhance the RF port ESD performance by integrating solid-state ESD protection technology. The RF port human body model (HBM) ESD rating of the ADGM1004 switch has been increased to 5 kV. This level of ESD protection is a first for the MEMS switch industry.

Size comparison of ADGM1004 and typical electromechanical RF relay (four switches)

Integrated solid-state ESD protection is a proprietary ADI technology that achieves very high ESD protection with minimal impact on the MEMS switch RF performance. Figure 3 shows an ESD protection component in an SMD QFN package. The die is placed on the MEMS die and connected to the RF pins of the package via wire bonds. These are optimized for RF and ESD performance.

In order to realize the ADGM1004 product, ADI not only inherited all the performance of the ADGM1304, but also combined three proprietary lithography technologies with assembly and MEMS capping technologies to achieve this performance breakthrough.

Compared with electromechanical relays, the highly reliable ADGM1304 and ADGM1004 can increase the cold switch life cycle by 10 times, while extending the working life of the ATE system and reducing costly downtime caused by relay failures. In addition, the ADGM1304 and ADGM1004 MEMS switch packages are extremely low in height, allowing designers to surface mount devices on both sides of the ATE test board to increase channel density and reduce costs without increasing the size of the equipment.

It has been two years since the release of these two revolutionary MEMS switches. ADI has also been committed to the development of MEMS technology. Click " Read More " to learn more about MEMS~

Thumbs up for the breakthrough ADI MEMS switch !