Ultra low actuation voltage RF MEMS switch
© Attaran and Rashidzadeh. 2015
Received: 6 May 2015
Accepted: 4 August 2015
Published: 11 August 2015
In this brief a new low actuation voltage RF MEMS switch is presented which can be integrated and controlled with available CMOS technologies. Despite the advantages in the design of RF MEMS switches designing a low actuation voltage RF MEMS switch is still a challenging task. To overcome this problem, a small size RF MEMS switch utilizing a moving plate with multiple holes supported by a low spring constant beam is presented in this work. Experimental measurement results indicate pull-in voltage of 0.5 V and lift-off voltage of 0.3 V for 1.5 μm displacement. The measured return loss and insertion loss are better than −20 dB and −0.1 dB respectively for a frequency range extending from 3 kHz to 3GHz. The switching time is less than 0.22 ms when the switch is turned on with a CMOS buffer from TSMC-65 nm technology with 1.00 V supply voltage.
KeywordsRadio frequency micro-electro-mechanical-system (RF MEMS) switch Low actuation voltage Microfabrication
Micro-Electro-Mechanical Systems (MEMS) devices have been vastly employed for many applications including Radio-Frequency (RF) components such as RF switches, variable capacitors and inductors [1–4]. RF and microwave MEMS switches have been subject of many research studies due to their superior performance such as high isolation, low insertion loss, good linearity and low power consumption. MEMS switches are either direct-contact style or capacitive type. Direct-contact MEMS switches are commonly used for application where the frequency of operation is limited to a few gigahertz. Capacitive switches are preferred for higher frequencies. To close or open MEMS switches the force is applied through electrostatic, magnetic fields or thermally induced forces . RF MEMS switches mostly employ electrostatic actuation due to low power consumption and short switching time as well as compatibility with electrical circuits and components. Electrostatic MEMS switches require a relatively high actuation voltage to drive the movable part. For the purpose of wireless communication or integrated circuit design, it is highly desired to reduce the pull-in voltage of MEMS switches. Various design techniques are proposed in the literature to reduce the actuation voltage. In  a pull-up type RF MEMS switch with low actuation voltage of 4.5 V is presented. In , a mechanically coupled low-voltage electrostatic resistive RF multithrow switch with 15 V is proposed.
In general, low actuation MEMS switches suffer from a range of problem including stiction, dielectric charging, hot switching life time and low power handling. In the proposed application in this work, a minute amount of power passes through the MEMS switch and thus the power handling and hot switching life time are not important issues. However, stiction and holding can affect the tag operation. The design of the MEMS switch has to be optimized to reduce these undesired effects.
In this work, a helix restoring spring is utilized to implement a low actuation voltage RF MEMS. The implemented switch includes a moving plate with multiple square holes that contribute to the faster operation of the switch by reducing the air damping factor under the moving plate. The dimple is added to reduce the gap between the movable plate and the output transition line to lowers the actuation voltage. A low-cost MEMS microfabrication process has been used to fabricate the MEMS switch. The implemented switch can be integrated with available 1.00 V supply CMOS technologies.
Mechanical and RF design principles
The Cr layer is used as an adhesion layer for Au which is washed out later. The fabrication process is followed by 0.7 μm SiO2 PECVD deposition at 250 ° C as dielectric. A 30 nm TiW is used at this step as an adhesion layer between D2 and G1. In step five a 2.5 μm thick spin coated polyimide layer is used as a sacrificial layer. To create the anchor and the dimple holes, polyimide is patterned using RIE. Then the fabrication process is completed by sputtering the 70 nm Au as a seed layer and an electroplated Au layer with total thickness of 2 μm and removing the sacrificial layer using O2 plasma dry etching in RIE.
Simulation and measurement results
Comparison of key features
Insertion loss (dB)
Return loss (dB)
1 V CMOS technology
8 × 108
1 × 107
1 × 104
400 × 100 μm2
2000 × 1000 μm2
1264 × 635 μm2
(Lower contact pad)
(Including biasing pads)
This paper presents a new low actuation voltage RF MEMS switch. A helix restoring spring together with a moving plate containing square holes are used to lower the pull-in voltage. A prototype is fabricated as a proof of concept using a fabrication process with seven electron-beam-write chromium masks. The switch is designed and optimized using Coventorware™. Measurement results indicate a pull-in voltage of 0.5 V which makes the switch ideal for integration with available low voltage CMOS technologies. It also presents −0.1 dB insertion loss and less than −20 dB return loss over a frequency range extending from 3 kHz to 3 GHz.
Complementary metal-oxide semiconductor
High resistivity traces
Plasma enhanced chemical vapor deposition
Reactive ion etching
Finite element analysis
The authors would like to thank the research and financial supports received from Natural Sciences and Engineering Research Council (NSERC) of Canada and CMC Microsystems.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Attar SS, Setoodeh S, Mansour RR, Gupta D (2014) Low-Temperature Superconducting DC-Contact RF MEMS Switch for Cryogenic Reconfigurable RF Front-Ends. IEEE Trans Microw Theory Tech 62:1437–1447. doi:10.1109/TMTT.2014.2327205 View ArticleMATHGoogle Scholar
- Rajagopalan H, Kovitz JM, Rahmat-Samii Y (2014) MEMS Reconfigurable Optimized E-Shaped Patch Antenna Design for Cognitive Radio. IEEE Trans Antennas Propag 62:1056–1064. doi:10.1109/TAP.2013.2292531 View ArticleGoogle Scholar
- Daneshmand M (2006) Multi-Port RF MEMS Switches and Switch Matrices. Dissertation, University of Waterloo. http://hdl.handle.net/10012/878
- Rebeiz GM (2003) RF MEMS: Theory, Design, and Technology. Wiley, Hoboken, NJView ArticleMATHGoogle Scholar
- Lee SD, Jun BC, Kim SD, Rhee JK (2005) A novel pull-up type RF MEMS switch with low actuation voltage. IEEE Microw Compon Lett 15:856–858. doi:10.1109/LMWC.2005.860006 View ArticleGoogle Scholar
- Kim CH (2012) Mechanically Coupled Low-Voltage Electrostatic Resistive RF Multithrow Switch. IEEE Trans Ind Electron 59:1114–1122. doi:10.1109/TIE.2011.2159694 View ArticleGoogle Scholar