June 3, 2023

Photo: SFedU press service

SFedU has developed switches for radio systems and networks 5G, which are superior in characteristics to foreign analogues. The results of the project will create a modern element base for the design and deployment of a mobile radio communication network applicable in the aerospace, defense, telecommunications and automated test industries. There were no similar analogues on the Russian market before.

Radio frequency microelectromechanical (MEMS) switches are compact devices that have low power consumption and can be fabricated using microelectromechanical systems (MEMS), usually various variations of surface technology. They operate on the principle of traditional light switches in a room, in which, when mechanical action is applied to certain areas of the housing, the contacts open or close, and thereby the electrical circuit to transmit an electrical signal through the switch. However, in the case of RF MEMS switches, its mechanical components are at the micrometer level. The signal transmitted through them is mainly in the region of microwave frequencies (SHF) – from 3 to 30 GHz. The radio frequency range depends on the application of the switch, for example, in radio devices and in equipment used in the aerospace, defense, telecommunications and automated test industries.

The idea of ​​using MEMS switches dates back to 2001, when UC San Diego professor Bing Binh Nguyen presented research on the use of MEMS technology in radio frequencies for mobile phones. Nguyen pointed out that the use of MEMS technology will improve performance, minimize the size and cost of RF filtering, integrate multiple functions on a single chip, and reduce power consumption. In addition, he concluded that these technologies can be used to create multi-frequency switches, microelectromechanical resonators and splitters on a silicon substrate. These features have been able to provide improved performance for mobile phones, as well as reduce their size and cost. Since then, MEMS technologies have been adopted by the mobile technology industry and are used in many devices today, including mobile phones, smartphones, tablets, and other devices.

According to the specialist, today the demand for RF MEMS switches is increasing due to the growing investment in the infrastructure of telecommunications networks. One of the fundamental reasons for this is the development and transition to standard fifth generation (5G) mobile radio communications. One of the fundamental and important components in a radio transceiver [прим. приемопередатчик] 5G are passive components made using MEMS technology, including RF switches. Their power consumption, RF performance, switching time, maximum RF transmit power and reliability directly affect the performance of radio systems and subsystems.

In modern radio devices, RF MEMS devices should have high isolation, low loss and crosstalk, switching time should not exceed 1 ms, and the control voltage should not exceed a few volts. MEMS technologies make it possible not only to adhere to this specificity, but also to combine various functionalities, which opens up interesting prospects in terms of reducing hardware complexity.

Employees of the Design Center for Microelectronic Component Base for Artificial Intelligence Systems and the SFedU Advanced Engineering School “Cyberplatform Engineering” Alexey Tkachenko, Igor Lysenko And Andrey Kovalev investigated a number of problems that arise in the design of RF MEMS switches and developed experimental models of switches with a capacitive switching principle.

“In MEMS switches with a capacitive switching principle, the movable electrode contacts the microwave line of the coplanar microwave waveguide used by means of a thin dielectric layer. MEMS switches with this switching principle do not work well at low frequencies, but in the RF and microwave bands they are superior to resistive MEMS switches. For this reason, capacitive MEMS switches are preferred for many applications, including radio systems and networks 5G. The main characteristic of a MEMS switch with a capacitive switching principle is the ratio of capacitances in the closed and open states (CON/COFF), and the higher this parameter, the more efficient the switch works. Therefore, MEMS developers are trying to increase CON and decrease COFF. A feature of this development is the use in the design of capacitive MEMS switches of an additional metal electrode with a floating potential and a thin dielectric layer with a high dielectric constant (TiO2). This approach to the design of capacitive MEMS switches makes it possible to increase the capacitance ratio in the closed and open states by more than an order of magnitude compared to classical approaches to the design of capacitive MEMS switches, – said the head of the Design Center for Microelectronics of the Southern Federal University Andrey Kovalev.

The developed experimental samples of MEMS switches are structurally distinguished by different types of movable electrodes: with a longitudinal and transverse arrangement of the movable electrode with respect to the microwave line of the coplanar waveguide used, with through holes of various geometries in the movable electrode (square, round) and without them at all. They can be used in radio frequency systems of 5G mobile networks, in relation to the 5G NR FR1 frequency band (up to 6 GHz) with a center resonant frequency of 3.4 GHz and 3.6 GHz.

Through holes in the movable electrode were made in order to reduce internal stresses in this metal layer, to better remove the sacrificial photoresist layer, to reduce the damping coefficient of the movable electrode in order to increase the switching speed – to reduce the time of closing / opening operations, – explained Andrey Kovalev.

The development of SFU differs significantly from the standard technology for manufacturing solid-state RF switches based on PIN diodes and FET transistors on GaAs substrates. For example, scientists use photoresist burning in oxygen plasma to remove the sacrificial (removable) layer of photoresist from under the moving electrode of an RF MEMS switch. Unlike foreign analogues, the new method of manufacturing RF MEMS devices has only one stage of deposition of a sacrificial layer, which eliminates the need to use selective etchants, a combination of liquid and dry etching, and also avoids sticking of moving elements in switches, which was previously observed in other technological processes. manufacture of such devices.

“Single-pole unidirectional RF MEMS switches manufactured by us are designed to work in radio systems and subsystems of mobile networks 5G for frequency range 5G NR FR1. They are characterized by high speed (<10 µs), low control voltage (3-5 V) and significantly better RF performance compared to existing foreign counterparts such as Analog Devices Inc. and Menlo Micro Inc. It should be noted that there are no analogues in the Russian market”, – commented the specialist.

The results of the study make it possible to create a modern electronic component base based on radio frequency MEMS technologies for the purpose of application in systems and subsystems of radar and communication systems in radio equipment for aerospace, defense, telecommunications and automated test purposes.

One of the promising areas of application of the results of the study is the design of radar and communication systems that are controlled using phased antenna arrays with a high directivity pattern (APAA), including electronically controlled phase shifters. They are based on RF MEMS switches. Considering that APAA of radar and communication systems can contain hundreds, thousands and even millions of elements, each of which contains a phase shifter, the main technical parameters of the antenna system are highly dependent on the characteristics of the phase shifters.

“Radar and communication systems with AFAR today are synonymous with the development of military equipment and radio electronics. At the same time, the development of AFAR technologies for missile defense systems has a serious military advantage due to its high gain and fast scanning beam. Thanks to the combination of powerful transmitters and huge electrically scanned radar arrays, this type of radar has extremely high transmit power and a variety of space scanning capabilities.” – said the specialist.

The results of a scientific project carried out within the framework of the state task on the topic “Development and research of methods and tools for monitoring, diagnosing and predicting the state of engineering objects based on artificial intelligence” were published in the journal micromachines.

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