rf mems switch design (comsol 4.2a)

Topics: MEMS, 4.2a, 4.3

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Amey Revandkar

Amey Revandkar

April 14, 2013 9:09am UTC

rf mems switch design (comsol 4.2a)

HeLLO,
i'm working on designing a switch that should work on rf range. I'm able to draw 2d structure in work plane but still not able to fix one side of the cantilver beam. i hve following questions,

1) When i drawn a random structure i was able to get domains and boundaries, but when i restricted dimensions at micron scale, i didnt found domains, only i was able to get 11 boundaries, plz help me in knowing how to fix one side of the beam on anchor...

2) moreover when i chose xy plane in workplane how to add dimension of device in z plane? i had worked on quick plane section in workplane but i'm fiding extremely difficult to draw structure at micron scale. i'm working on coplanar waveguide .

kindly help

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Ivar Kjelberg

Ivar Kjelberg

April 14, 2013 9:56am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

the CAD feature of COMSOL are not as advanced as those you can find in a full blow 3D CAD software (not the same purpouse). For elevation from a plane (extrusion) you can define only one height per node (note I havent really checked if I can add an array, as for copy ... but anyhow it extracts all objects to that/those heights

And when you have really very small scales, check the units and the relative resolution features (also of the graphics rendering as sometimes the geometry is OK, but the graphics rendering is poor, this happens seldom or me)

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

April 15, 2013 8:10am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Thanks sir,
i'm finding it out extremely difficult to simulate the structure ..please can u suggest any other alternative to get the structure drawn at micron scale. .

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Ivar Kjelberg

Ivar Kjelberg

April 15, 2013 8:52am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi
Use the geometry scale set in microns, and also make a new Definition View2, go to the sub node "Camera" and turn off "Preserve Scale ratio"

Then you can switch easily between view 1 and view 2

If you have a large bulk block you can hide it in view 2 by adding a sub-node Hide "Entities" and select the large "thick" structure(s)

This often helps for MEMS modelling ;)
--
Good luck
Ivar

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Fandi Hamid

Fandi Hamid

April 15, 2013 1:29pm UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Hallo, i'm new using the comsol software.anyone can help me how to modeling the shunt capacitive mems switch?

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Amey Revandkar

Amey Revandkar

April 18, 2013 7:13am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Thanks sir,
I did simulate my structure on cantilever and i obtained following results for study type eigen frequency in solid mechanics model:

in 3D plot group first 4 eigenfrequencies,

1. -93983.02i

2. -93983.0354i

3. -3.128e5i(1)

4. -3.12897e5i(2)

i dont know to interpret these reults.
morover in solver configuration ,in dependant variables subnode, in initial variables solved for under 3subnode Eigenfrequencies
i obtained 4 eigenfrequencies but only one eigenmode was shown..r these results authentic?
kindly help,
regards.

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Ivar Kjelberg

Ivar Kjelberg

April 18, 2013 9:06am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

are you sure those are the "eigenfrequencies, and not the eigenvalues ?

Check the solver name, and your doc, as there are both ;)

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

April 22, 2013 5:59pm UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

hi,
This time i got 4 eigenfrequencies without imaginary part. i beleive it must be correct. i hve following querries:

1. i hve simulated the cantileverbeam on the substrate and found eigenfrequencies, length of the beam is 70 micron,
thickness is 3 micron,but the width is in z direction and i want to measurethat. plz let me know how it can be done?

2. what will be the unit for eigenfrequency?

i'm attaching the file hereby
Regards

Attachments:   ef4.pdf  

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Ivar Kjelberg

Ivar Kjelberg

April 23, 2013 9:11am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

you solver says eigenvalue ? I suspect something has been messed up in the solver sequence, try making a new study with an Eigenfrequency solver, this could explain the complex results

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

April 23, 2013 7:33pm UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

hi,
i'll check the solver sequence, meanwhile i have calculated the spring constant of the cantilever beam which is0.0036.
the dimensions are,
length = 70 micron
width= 1 micron
thickness =0.3micron
is the value correct?

also can i know what could be the simplest formulae to find first eigenfrequency/free running frequency for above dimensions?
regards

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Ivar Kjelberg

Ivar Kjelberg

April 24, 2013 9:35am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

the physics formulas do not change with scale at most the cuplings due to the change in volume to area ratio. So take any valid canteliever beam formula and enter your dimensions and material properties E, nu, rho

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

April 30, 2013 6:27pm UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Hi,
May i know if the results of my simulation for cantilever beam are correct or not for the given data:
L= 90 micron, W=40 micron, thickness t= 0.3 micron for aluminium cantilever with E= 70 GPA, poissons ratio=0.35,Density=2700 kg/m3,

results:

spring constant= 0.025

pull down voltage= 11.12 V

eigen frequency1= 31486.5373 ef2= 1.48e5, ef3= 1.9655e5, ef4= 4.7977e5

regards

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Ivar Kjelberg

Ivar Kjelberg

April 30, 2013 6:44pm UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

if you check on wikipedia the single sided fixed-free beam deflection tells you F/disp = 3E*I/L^3 where F is the force applied, disp the tip displacement, E the young modulus, L the beam length and I the Area moment of inertia typically some thing like "tickness^3*width/12" for a rectangular section beam deflecting along an axis paralle to the width

Another rule of thumb I often use is the maximum deflection "disp" of the first fundamental mode frequenacy "f" often follows

2*pi*f = sqrt(k/m) = sqrt(g/disp)

where g=9.81[m/s^2], m the mass bt often one take 2/3 of the total beam mas in a fixed-free case

But you fins also more precise formulas on Wiki i.e Euler - Bernoulli beam or in the COMSOL doc theory section

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

May 1, 2013 12:24pm UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Thanks sir,
I have used the same formulas u stated above and i got the the mentioned results. Now i'm performing Electromechanics modelling to check displacement for the actuation voltage i obtained.

As i'm using comsol 4.2a i'm following the instructions given under resonator study model pdf. with necessary instructions relevant to my model. i request you to kindly check the mph file attached hereby and help me in modelling as i have just 7 domains in my structure.

regards

Attachments:   aluminium bias voltage.mph  

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Ivar Kjelberg

Ivar Kjelberg

May 1, 2013 1:21pm UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

I see you have a challenging model there.
For me my main comments are that to get a electrostatic field to develop, you must include some "air" or vacuum between the electrodes, and also above to allow the field to loop around

As you model is basically an extruded 2D model it would be far simpler and faster to work in 2D and define the appropriate depth d (along Z) for the absolute values calculations. I can only recommend to start "simple" in 2D then go to 3D.

Even have you started in 2D structural alone,m checked your eigenfrequencies, the material selections etc, often useful. But if you are well used to COMSOL then jumping straight into EMI is possible.

Finally you could reduce the solid AlO3 block to have less elements to mesh, and to allow for at least 3-5 mesh elements in the thickness of your thin beams to correctly resolve what is happening in the beam/plates you have

--
Good luck
Ivar

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Amey Revandkar

Amey Revandkar

May 2, 2013 10:45am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Hii,
Thanks indeed for the previous reply. I'm still trying to get the EMI perfect. meanwhile i'm trying to find the biased modes .i.e. i'm trying to apply 11 V dc bias voltage and trying to get the biased mode shapes.
Will u please go through the file i'm attaching hereby that has the unbiased modes and help me in getting biased shapes for 11 V.

Regards

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Amey Revandkar

Amey Revandkar

May 2, 2013 10:47am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

here is the file attached

Attachments:   final aluminium.mph  

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Ivar Kjelberg

Ivar Kjelberg

May 3, 2013 5:31am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)

Hi

when you look at your results you see that basically what is of interest for the eigenfrequency is only domain 5 or perhaps 3+5

if you domain 6 is a counter electrode you could add some boundary load on the beam domain 5 by estimating the force you would get from your voltage, the distance the related areas, and then do a pre-stresssed eigenfrequency analysis (stationary + eigenfrequency linearised from the stationary result, compare to a linear buckling analysis to see how the solvers are combined)

If you want to add ES and ES forces you need to add the surrounding air/vacuum above and below your electrode. This can also be done in EMI

I have only latest version so I cannot make any "older version models" but I'm sure you will get there easily

--
Good luck
Ivar

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Sarath Gopalakrishnan

Sarath Gopalakrishnan

July 4, 2013 6:26am UTC in response to Amey Revandkar

Re: rf mems switch design (comsol 4.2a)


Hi,
May i know if the results of my simulation for cantilever beam are correct or not for the given data:
L= 90 micron, W=40 micron, thickness t= 0.3 micron for aluminium cantilever with E= 70 GPA, poissons ratio=0.35,Density=2700 kg/m3,

results:

spring constant= 0.025

pull down voltage= 11.12 V

eigen frequency1= 31486.5373 ef2= 1.48e5, ef3= 1.9655e5, ef4= 4.7977e5

regards


Hi, I have been trying to find out the pull in voltage of a very basic cantilever based MEMS switch. I referred to the tutorial given in MEMS module for resonator pull in voltage calculation and tried to simulate a switch. However, I keep getting errors indication lack of convergence and NaN/Inf not found and so on. Were you successful in finding out the pull in voltage? I would appreciate it if you help me by giving some tips on this issue.

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Amey Revandkar

Amey Revandkar

July 18, 2013 10:24am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Sir,
I'm getting spring constant for my cantilever beam as low as 0.025N/m . so just want to know wheather the spring constant value can be as low as this. The dimensions for my beam are l=90micron, W=40micron, t=0.3micron,E=70Gpa for aluminium.

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Amey Revandkar

Amey Revandkar

July 24, 2013 11:47am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Dear sir,
I'm doing Stationary Analysis for checking the displace ment of cantilever beam(RF Switch) . Ihave almost reachead the end of the modelling , but getting error like,'' Failed to evaluate the expression''. I request you to therefore help me out in completing the analysis. I'm attaching the file hereby,
Regards

Attachments:   july 24.mph  

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Yu Y.Y

Yu Y.Y

September 18, 2013 11:18am UTC in response to Ivar Kjelberg

Re: rf mems switch design (comsol 4.2a)

Hi,Ivar
Now I am trying to use emi physics to make a MEMS capacitor with vacuum sealed gap. The top plate of capacitor is thin as compared with the diameter. So the top plate(membrane) will be deflected to the bottom plate due to the surrounding air pressure. I have tried a way by adding material with relative permitivity of 1 in the gap. But the membrane did not deflected more as compared with the air inside the gap. Is there any wrong with this method?
Thank you very much!



Hi

when you look at your results you see that basically what is of interest for the eigenfrequency is only domain 5 or perhaps 3+5

if you domain 6 is a counter electrode you could add some boundary load on the beam domain 5 by estimating the force you would get from your voltage, the distance the related areas, and then do a pre-stresssed eigenfrequency analysis (stationary + eigenfrequency linearised from the stationary result, compare to a linear buckling analysis to see how the solvers are combined)

If you want to add ES and ES forces you need to add the surrounding air/vacuum above and below your electrode. This can also be done in EMI

I have only latest version so I cannot make any "older version models" but I'm sure you will get there easily

--
Good luck
Ivar

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