Design and simulation of mems shunt capacitive switch for lower switching time

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DESIGN AND SIMULATION OF MEMS SHUNT CAPACITIVE SWITCH

FOR LOWER SWITCHING TIME

Kurmendra

Department of Electronics & Communication Engineering,

Rajiv Gandhi University, Itanagar, (India)

E-mail: kurmendra.nits@gmail.com

Rajesh Kumar

Department of Electronics & Communication Engineering,

North Eastern Regional Institute of Science & Technology, Itanagar, (India)

E-mail: itsrk2006@gmail.com

Design and simulation of mems shunt capacitive switch for lower switching time

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ABSTRACT

As Demand of High speed devices increasing for RF and satellite

communications with better accuracy, MEMS technology is considerd to be

emerging technology to fulfill that need. In this paper, A MEMS shunt

capacitive switch with fixed- fixed beam have been designed and simulated for

numerous parameters. The parameters for study are Selection of beam

material for the switch, air gap distance between electrodes and importantly

the actuation voltage. For studying the effect of air gap and beam width on

switching time , the air gap was varied from 0.6 µm to 2.0 µm and beam width

from 1 µm to 50 µm. For an actuatiuon voltage of 10.5 V and air gap distance

of 0.6 µm, switching time result is 0.2 ns for spring constant equal to gold

material.Study also considers the effect of increasing beam dimension in terms

of width for a constant gap height. This syudy will be helpful for designing a

MEMS capactitive switch for higher speed and for selection of proper

dimension to get better performance.

KEYWORDS

Beam, Electrode, MEMS, RF, Switch, Switching time.

1. BACKGROUND

RF MEMS switches are considered to be a potential switching device for high

speed switching applications. These types of switches have capability of

replacing traditional MOSFET switch, Tunnel Switch and Pin-diode based

Switch [1-4]. Many actuation mechanisms such as optical actuation,

electrostatic actuation, thermal actuation and actuation by force are used for

MEMS switch devices [5]. Mostly used actuation mechanism is Electrostatic

actuation since it has many practical advantages such as low power

requirement and small sized device. Despite of having various advantages,

MEMS switches lack in switching speed and requirement of low pull in voltages

[6-7]. Various techniques are currently being used to overcome the problems

associated with these switches. Low spring constant materials are considered

to be prominent source of material for low pull in voltage but at the same time,

the switch suffers with low speed and reliability of device [8-9]. The switching

speed can be increased by using a switch beam with lower mass. The switches

made up of low mass materials relatively posses high speed compare to higher

spring constant materials [10]. A. Kundu et al. (2010) have designed a new

switch where the top metal and central conductor both are movable and

considerable improvement was found in actuation voltage requirement and

switching time as 20 % down [11]. S. Sekhar et al. (2011) designed

electrostatically actuated MEMS switch and experimental as well as FEM

analysis were done. Their observation concludes that pull up time is more than

pull in time which is somewhat counter part because in case of pull in there is

much larger electrostatic force compare to pull up restoring force at release

time [12]. C. Siegel et al, have provided the switching analysis of MEMS

cantilever-based switch and article reports that measured switching time in the

air medium for the switch is below 75 µs which is also dependent of actuation

voltage. Semiconductor effect in actuation path is responsible for 60 µs and

switching time also depends on bending of the membrane [13]. Markus et al

Design and simulation of mems shunt capacitive switch for lower switching time

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(2014) have reported that they have designed a MEMS switch which requires

very low pull in voltage as 5V and switching time is less than 10 µs at 5 Ghz.

The designed switch is very much usable for RF applications [14]. K. Guha et

al. (2015), have proposed meander-based switch made up of Aluminum

membrane and the study was done for providing very less switching time as 3

µs for actuation voltage of 5V [15]. K. Guha et al. (2018) have also proposed a

new analytical model for analysis of switching time for perforated MEMS

switch. They have presented modified Mejis and Fokkema’s model and the

model is capable of evaluating switching time for uniform as well as non-

uniform meander-based switch designs. Results were plotted between

switching time and displacement for uniform and non-uniform meander

designs with different Vs and materials [16].

In this article, a Shunt capacitive MEMS switch is designed which is capable of

working at very high frequency range 20- 100 Ghz approximately.. The MEMS

switches have also been designed by other researchers having different kind of

structures. But these designed switches have many disadvantages such as

insertion loss, isolation loss, return loss and very important switching time.The

previously published articles in the domain have addressed about losses

associated with their designed switches but only a few articles have presented

switching time analysis [refer table.2 ]. Firstly, the structure presented in this

paper was optimized in terms of different size dimensions as well as the

selection of materials involved a rigorous literature review and were so chosen

that the disadvantages associated with previously designed switches could be

overcome [17-18]. After designing the switch, we have done many static

analysis such as pull in voltage analysis and RF analysis which have already

been published in a journal of repute [21]. We found that the designed switch

is showing a great improvement in terms of insertion, isolation and return loss

parameters [21] Here, An analysis of the MEMS switch considering switching

time is presented in terms of dielectric constant, voltages, air gap and width of

the beam material.

In the proposed work we have taken most promising issue related to the

MEMS switch that is switching time. Our work has shown tremendous

improvement in terms of switching time as well as losses associated with. The

switch designed on MEMS technology generally have one disadvantages of

having larger switching time which has been significantly improved and which

is presented in the paper.

2. DESIGN OF PROPOSED MEMS SHUNT SWITCH AND WORKING

Figure 1. Schematic of proposed RF MEMS shunt switch.

Design and simulation of mems shunt capacitive switch for lower switching time

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The schematic of designed MEMS shunt switch is shown in the Figure1. The

switch consists of silicon substrate, dielectric layer (Si3N4) placed over CPW

transmission line and gold material is used for beam bridge, beam supporting

anchors and transmission line central conductor as well as CPW ground. There

is an air gap g0 between Au top electrode and dielectric layer above CPW signal

line. The switch is actuated by using very common actuation technique that is

electrostatic actuation. Initially there will not be applied any actuation voltage

and the signals in the signal line go without any interruption. When a voltage

is supplied between beam and down electrode (CPW signal line) as shown in

fig.1, an electrostatic force is developed on switch membrane (beam) and this

force pulls down the beam. When this beam touches dielectric material, it

forms a path between signal line and beam to the CPW ground for signals

coming from CPW signal line, thus signal goes to CPW ground, the switch is

called to be in OFF state. In the actuation and switching analysis, the supply

voltage, air gap and material properties play very important role.

3. FORMULATION & SWITCHING PERFORMANCE ANALYSIS

RF MEMS switch generally offers a better performance characteristic when

considered for low insertion loss, high isolation and low return loss. The

performance characteristics of the switch does not only depend on these losses

but also depends on the speed to make open and close circuit, generally

termed as switching speed. Switching speed can be improved by employing

different techniques such as TMPS technique [11] where the electrode as well

as signal conductor move to offer a better switching speed. In this section, we

are going to include some important switching equations for switching time

analysis.

The switching time in terms of applied voltage (), pull in voltage () and

operating frequency can be given as [19]







(1)

Where,  is the switching time of the designed switch,  is the pull in voltage

(10.5 V), Vs is the supplied voltage () and is the operating

frequency or resonance frequency of the switch. Spring constant of the

material specifically used for switch membrane is important parameter for the

switching time analysis of the switch. An equation for switching time in terms

of spring constant of beam membrane can be obtained by putting 

and 











[16]













(2)

Where, ‘’ is the effective mass and ‘’ is the spring constant of the beam

membrane for the designed switch.

The switching time in terms of gap height g0 and width of the membrane can

be approximated and give as [11]





















(3)

Design and simulation of mems shunt capacitive switch for lower switching time

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Where, 𝑔0 is the initial airgap between the membrane and signal line, Ɛ0 is the

free space permittivity and 𝑊 is the width of the switch beam membrane.

The equations which are provided above helps in analyzing the switch

performance in terms supplied voltage, spring constant, air gap heights and

width of the top metal beam.

4. RESULT & DISCUSSIONS

A MEMS capacitive shunt switch was designed as shown in the Figure 1. The

design parameters and materials used in the proposed switch is given in the

Table.1. The operating frequency of the switch was calculated using coplanar

waveguide calculator [20] and was verified using COMSOL Multiphysics 5.1

software.

Table 1. Design parameters and materials used of the proposed switch.

Serial number

Design Parameter

Value (in µm)

Materials used

Beam length

100

Gold

Beam width

Beam thickness

Gold

Coplanar wave guide

50-10-1

Gold

Dielectric thickness

0.4

Si3N4

Substrate thickness

Air gap

Supply voltage for

switching analysis (𝑉𝑠=

1.4⁡𝑉𝑝)

Operating frequency

0.6

14.7 V

62 Ghz approx.

Silicon

-------

--------

Figure 2. Switching time variation in terms of applied voltage (Vs = 1.4 Vp).

In the Figure 2, result for switching time for the sweep of 0-15 V in supply

voltage is given. From the plot we can understand that in the voltage range 0-

5 V, switching time is more compare to switching time for 5-15 V. our designed

Design and simulation of mems shunt capacitive switch for lower switching time

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switch posses pull in voltage about 10.5 V for which we obtain the switching

time as low as 0.2 ns.

Figure 3. Switching time variation for varying spring constant of beam material.

Figure 3 illustrates, the curve between spring constant for the beam material

and switching time. It can be clearly concluded that the switch made up of high

spring constant value is going to require very less switching time compare to

beam materials with low spring constant thus enables switch to work at high

speed.

Figure 4. Switching time as function of varying air gap height between beam electrode and

dielectric layer above signal line.

Design and simulation of mems shunt capacitive switch for lower switching time

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Figure 4 depicts the result between the air gap heights and switching time for

designed switch, as per the literature the lower the gap between top and

bottom electrode demands lower switching time but lowering of this gap is

permissible only up to certain limit since there should be enough gap to apply

supply voltage (𝑉𝑠=1.4⁡𝑉𝑝). In Figure 4 it can be observed that as we are

approaching towards higher air gap, the requirement of switching time is also

increasing which considerably reduces the speed of the switch.

Figure 5. Switching time variation for different beam width for air gap go,g1,g2 and g3 .

As per the equation (3) of the section.3, we can see that the beam width does

play an important role for switching speed or switching time of the device. In

the Figure 5, the result for varying width of the beam and switching time is

plotted for constant air gap (g0 = 0.6 um, g1 = 1.0 um, g2 = 1.5 um & g3 =

2 um). Arrow sign in the Figure 5 is kept for showing increasing air gap height

direction. as we keep on increasing the width of fixed- fixed beam of the switch,

the switching time required is getting lesser. While choosing greater beam

width, we should note that for a miniaturized device, there is need of using

beam with lesser beam width. The effect of increasing air gap between beam

electrode and lower electrode are considerably high for the same sweep of

beam width. In the Figure 5, it can be observed that as we are increasing this

gap the switching time requirement is going to be very high compare to lesser

beam width. Thus, there is a need for trade off between the switch parameters

such as air gap, beam width, applied voltage and selection of materials for

improving the switching time which ultimately improves the switching speed.

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Table 2. Compared results obtained with various losses, Frequency of operation and switching

time.

Sr. No.

Insertion

loss

Isolation

Return

loss

Switching

time

Frequency

operation

References

0.29 dB

20.5 dB

-------

Not done

35 Ghz

Muhua li et al

[2017] [22]

-0.4 dB

80 dB

-------

Not done

20 Ghz

Guha et al.

[2016] [23]

-0.44 dB

- 20 dB

- 16 dB

Not done

0.6 – 40

Ghz

T. Laxmi

Narayana et

al [2017] [24]

-------

--------

---------

< 10 us

5 Ghz

M. Gatzsch et

al [2014] [14]

-0.05 dB

-12 dB

-45 dB

0.2 ns

61.5 Ghz

Our work

A comparision have been shown in Table 2 between our designed MEMS shunt

capacitive switch and switch reported in other articles. Through comparision

it was found that our designed switch results in a much improved performance

in terms of losses and switching speed.

5. CONCLUSION

The paper presents the performance analysis of a new and simple shunt

capacitive switch design in terms of switching time. The analytical equations

were presented for the analysis. Specifically switching time was analytically

analyzed on four parameters such as supplied voltage, spring constant of

material, initial air gap heights and width of the material. From the analysis of

the results, it can be concluded that trade off between supply voltage and

switching time is required since high switching is achieved for high supplied

voltage but a device with high supply voltage is not recommended. High

spring constant materials results in less switching time which practically

improves switching speed. A switch with larger beam width and lesser air gap

is efficient for high switching speed. This study will surely be useful for

researchers working in the area of MEMS switch design for high frequency

applications.

6. ACKNOWLEDGEMENT

This research work has been carried out in MEMS laboratory, Department of

ECE, Rajiv Gandhi Central University, Itanagar, INDIA.

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7. REFERENCES

1. G.M. Rebeiz “RF MEMS Theory, Design and Technology”

Wiley, New Jersey (2003)

2. A. DeHon, "Array-based architecture for FET-based, nanoscale

electronics," in IEEE Transactions on Nanotechnology, vol. 2, no. 1, pp.

23-32, Mar 2003. doi: 10.1109/TNANO.2003.808508

3. F. Gentili, L. Urbani, G. Bianchi, L. Pelliccia and R. Sorrentino,

"PIN diode-based 4-channel switched filter bank with low-power,

TTL-compatible Driver," IEEE MTT-S International Microwave

Symposium (IMS2014), Tampa, FL, 2014, pp. 1-4. doi:

10.1109/MWSYM.2014.6848379

4. A. Chaney, M. Qi, S. M. Islam, H. G. Xing and D. Jena, "GaN tunnel

switch diodes," 2016 74th Annual Device Research Conference (DRC),

Newark, DE, 2016, pp. 1-2. doi: 10.1109/DRC.2016.7548409

5. B. G. Sheeparamatti, Prashant Hanasi, Vanita Abbigeri, “Critical

Analysis of Different Actuation Techniques for a Micro Cantilever”,

World Academy of Science, Engineering and Technology

International Journal of Mechanical and Mechatronics Engineering

Vol:9, No:11, 2015.

6. M. Solanska, M. Markovic and M. Dado, "Time analyses of S-

RFORP and S&C reservation protocols in optical networks with 2D

MEMS switches," ELEKTRO, Strbske Pleso, 2016, pp. 88-91. doi:

10.1109/ELEKTRO.2016.7512041

7. Mahesh Angira, KamalJit Rangra, “A novel design for low insertion

loss, multi-band RF-MEMS switch with low pull-in voltage”,

Engineering Science and Technology, an International Journal,

Volume 19, Issue 1, 2016, Pages 171-177, ISSN 2215-0986,

https://doi.org/10.1016/j.jestch.2015.07.001.

8. C.-Liang Dai, H.-Ming Hsu, M.-Chang Tsai, M.-Ming Hsieh, Ming-

Wei Chang,

“Modeling and fabrication of a microelectromechanical microwave

switch”,

Microelectron. J. 38 (2007) 519–524

9. D. Hah, E. Yoon, S. Hong, “A low voltage actuated micromachined

microwave

switch using torsion springs and leverage”, IEEE Trans. Microwave

Theory

Tech. (2000) 2540–2545

10. Bonthu, M. & Sharma, A.K. “An investigation of dielectric material

selection of RF-MEMS switches using Ashby’s methodology for RF

Design and simulation of mems shunt capacitive switch for lower switching time

DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue.15

176

application”,s Microsyst Technol (2018) 24: 1803.

https://doi.org/10.1007/s00542-017-3539-x

11. A. Kundu , S. Sethi , N.C. Mondal , B. Gupta , S.K. Lahiri , H. Saha ,

“Analysis and optimization of two movable plates RF MEMS switch

forsimultaneous improvement in actuation voltage and switching

time”, Microelectronics Journal 41 (2010) 257–265

12. Shekhar, S , Vinoy , KJ , Ananthasuresh, GK ,”Switching and Release

Time Analysis of Electrostatically Actuated Capacitive RF MEMS

Switches”. (2011) In: IFSA, 130 (7). pp. 77-90.

13. C. Siegel, V. Ziegler, C. von Wächter, B. Schönlinner,U. Prechtel, H.

Schumacher, “Switching speed analysis of low complexity RF-MEMS

switches” https://duepublico.uni-duisburg-

essen.de/servlets/DerivateServlet/Derivate-

14694/Final_Papers/GM0029-F.pdf

14. Markus Gaitzsch, Steffen Kurth, Sven Voigt, Sven Has, Thomas

Gessner , “Analysis of Au metal–metal contacts in a lateral actuated RF

MEMS switch”, International Journal of Microwave and Wireless

Technologies, 2014, 6(5), 481–486

15. Koushik Guha, Prerana Roy, AnganaNath, Srimanta Baishya,

“Switching Time Analysis of MEMS Shunt Switch using MATLAB”,

2nd International Conference on Microelectronics,Circuits and

Systems,Micro2015.

16. K. Guha, N. M. Laskar, H. J. Gogoi, K. L. Baishnab, K. Srinivasa Rao,

“A new analytical model for switching time of a perforated MEMS

switch”, Microsyst Technol (2018). https://doi.org/10.1007/s00542-

018-3803-8

17. Kurmendra & Kumar, R. , “Design analysis, modeling and

simulation of novel rectangular cantilever beam for MEMS sensors

and energy harvesting applications” ,Int. j. inf. tecnol. (2017) 9: 295.

https://doi.org/10.1007/s41870-017-0035-6

18. Ashby, M. F., “Materials Selection in Mechanical Design”, 2nd

Edition, Butterworth-Heinemann, Oxford, UK, 1999.

19. A. K. Sharma and N. Gupta, "Switching time analysis for non-uniform

serpentine flexure based RF-MEMS switches," Students Conference on

Engineering and Systems (SCES), Allahabad, 2013, pp. 1-4. doi:

10.1109/SCES.2013.6547531

20. Coplanar Waveguide Calculator, http://

www.microwave101.com/encyclopedia

21. Osor Pertin, Kurmendra, “Pull-in-voltage and RF analysis of MEMS

based high performance capacitive shunt switch”, Microelectronics

Design and simulation of mems shunt capacitive switch for lower switching time

DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue.15

177

Journal, Volume 77, 2018, Pages 5-15, ISSN 0026-2692,

https://doi.org/10.1016/j.mejo.2018.05.001.

22. Muha li, Jiaho Zhao, Zheng You, Guonghong Zhao, “Design and

fabrication of a low insertion loss capacitive RF MEMS switch with

novel micro-structures for actuation”, Solid-State Electronics Volume

127, 32-37 (2017)

23. Koushik Guha, Mithlesh Kumar, Ajay Parmar, Srimanta Baishya,

“Performance analysis of RF MEMS capacitive switch with non

uniform meandering technique”, Microsyst Technol 22: 2633 (2016).

24. T. Lakshmi Narayana, K. Girija Sravani, K. Srinivasa Rao,Wei

Meng ” Design and analysis of CPW based shunt capacitive RF MEMS

switch”, Cogent Engineering, 4:1, (2017)

DOI: 10.1080/23311916.2017.1363356

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DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue.15

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