# Cantilever switch based on electrostatic force

• Si14
In summary: I think it could be about 0.5x0.5x0.5mm. And the reason is that when the switch is closed, the electric field would be concentrated on the contact area and it might damage the device.
Si14
Dear all:

I am going to design a cantilever switch which is working with electrostatic (capacitive) force.

I want to design that. That is to find the dimension and material of that.
I was wondering if you could kindly suggest a reference for designing this.

Thank you very much.

Hello Si14,

If you can supply a roughly dimensioned sketch, perhaps I can help. I've spent about 8 years of my life designing capacitance-based sensors and electrical interfaces. I know, I should probably get out more...

- Mike

Mike_In_Plano said:
Hello Si14,
If you can supply a roughly dimensioned sketch, perhaps I can help. I've spent about 8 years of my life designing capacitance-based sensors and electrical interfaces. I know, I should probably get out more...
- Mike

Hi Mike:

Thank you very much. Here is my design.

http://img23.imageshack.us/img23/4686/cantileverswitch.jpg​
[/URL]

As you can see, I want to use the Gate to turn the switch on/off.
The cantilever will bend and makes contact with the Drain.
For this design, First, I assume a=b (uniform width: simplest case)
For that case I assumed that the spring constant of the cantilever is k=(8EI)/(l^3)

So first, can I use this spring constant? Since I assumed that the force is distributed uniformly on the cantilever (the simplest case).

And also I used thepull-in voltage Vpi=sqrt[(8k*g^3)/(27*eps0*A)]
which can be applied to all capacitor cases.

So this is my 1st step. After hearing your comments, we'll go to next step.

Thanks a lot.

Last edited by a moderator:
Si14 said:
Hi Mike:

Thank you very much. Here is my design.

http://img23.imageshack.us/img23/4686/cantileverswitch.jpg​
[/URL]

As you can see, I want to use the Gate to turn the switch on/off.
The cantilever will bend and makes contact with the Drain.
For this design, First, I assume a=b (uniform width: simplest case)
For that case I assumed that the spring constant of the cantilever is k=(8EI)/(l^3)

So first, can I use this spring constant? Since I assumed that the force is distributed uniformly on the cantilever (the simplest case).

And also I used thepull-in voltage Vpi=sqrt[(8k*g^3)/(27*eps0*A)]
which can be applied to all capacitor cases.

So this is my 1st step. After hearing your comments, we'll go to next step.

Thanks a lot.

Can you give an order of magnitude for the dimensions of this cell? And can you say why you are shorting out the drain and source with the contact? Are you aiming to make some sort of a mechanical oscillator?

Last edited by a moderator:
berkeman said:
Can you give an order of magnitude for the dimensions of this cell? And can you say why you are shorting out the drain and source with the contact? Are you aiming to make some sort of a mechanical oscillator?

The dimensions are my question. I didn't shorten the D/S contact on purpose.
As I said in my previous post, this is a switch.

BTW, can you confirm the formulas which I gave previously (spring constant, Vpi)?
After that, I think I will be able to suggest some dimensions.

Thanks.

Si14 said:
The dimensions are my question. I didn't shorten the D/S contact on purpose.
As I said in my previous post, this is a switch.

BTW, can you confirm the formulas which I gave previously (spring constant, Vpi)?
After that, I think I will be able to suggest some dimensions.

Thanks.

In asking for target lithographic dimensions, I assumed that you had a particular IC geometry already in mind. In IC design, we generally have a target geometry (or small range of geometries) in mind when thinking about a new IC. But perhaps it is different in MEMS design:

http://en.wikipedia.org/wiki/Microelectromechanical_systems

As for the switch part, may I assume you are working on a MEMS relay of some sort? If so, you would not make the switch/relay out of a single MOSFET MEMS device. As I said in my previous post, it looks like the D-S would be shorted out by the closing of the switch. If you want to make a switch using MEMS electrostatic forces, then you will need to separate the attractive E-field from the switch closure. Why?

berkeman said:
In asking for target lithographic dimensions, I assumed that you had a particular IC geometry already in mind. In IC design, we generally have a target geometry (or small range of geometries) in mind when thinking about a new IC. But perhaps it is different in MEMS design:
http://en.wikipedia.org/wiki/Microelectromechanical_systems
As for the switch part, may I assume you are working on a MEMS relay of some sort? If so, you would not make the switch/relay out of a single MOSFET MEMS device. As I said in my previous post, it looks like the D-S would be shorted out by the closing of the switch. If you want to make a switch using MEMS electrostatic forces, then you will need to separate the attractive E-field from the switch closure. Why?
Thanks. I am using it for MEMS application, and also I have no target dimension. The dimension could be 1mm*1mm or less.
But this switch will work. Since I will know when the switch is on or off by measuring the current for example. So shortening between the drain and source is a part of switching mechanism.
Also, the electrostatic force is only used to pull the cantilever downward. So it is kind of different from other electrostatci switches using only two plates.

Si14 said:
Thanks. I am using it for MEMS application, and also I have no target dimension. The dimension could be 1mm*1mm or less.
But this switch will work. Since I will know when the switch is on or off by measuring the current for example. So shortening between the drain and source is a part of switching mechanism.
Also, the electrostatic force is only used to pull the cantilever downward. So it is kind of different from other electrostatci switches using only two plates.

What provides the holding force after the E-field is shorted out?

berkeman said:
What provides the holding force after the E-field is shorted out?

The E-filed between the GATE and cantilever is still available. Since it is not shorted. Drain is only for sensing the short circuit. Not driving the switch.

Hello,

I understand part of your equations, but I'm having difficulty with the entirety. For force, given voltage and ideal (square) surfaces, I get:

F=E^2 A Eps0 / 2 gap^2

Where F - Force, E - Applied voltage, A - area of the two plates, and gap - distance between plates

Given Force, this gives me:

E = sqrt(2 F gap^2 / A Eps0)

It looks like you substituted in the forces for beam deflection for F. Is this correct?

-Mike

Mike_In_Plano said:
F=E^2 A Eps0 / 2 gap^2

Given Force, this gives me:
E = sqrt(2 F gap^2 / A Eps0)
It looks like you substituted in the forces for beam deflection for F. Is this correct?
-Mike

Thanks.
In your first equation, I think, you should substitute E with V.

But I didn't drive that spring constant. I used a formula for simple cantilever under uniform pressure. And then since the maximum deflection is at x=L. So I derived the k.

Which is:

http://img12.imageshack.us/img12/4176/springconstant.jpg​
[/URL]

But I am not sure about the: Rho=F/L

So that's how I used that formula.

Last edited by a moderator:

## 1. What is a cantilever switch based on electrostatic force?

A cantilever switch based on electrostatic force is a type of switch that uses electrostatic force to control the movement of a thin, flexible beam or cantilever. The switch is typically made of a conductive material and is designed to bend or move when an electric field is applied. This movement can be used to open or close an electrical circuit, making it a useful component in electronic devices.

## 2. How does a cantilever switch based on electrostatic force work?

The cantilever switch works by using the principle of electrostatic attraction and repulsion. When an electric field is applied to the switch, the cantilever bends or moves due to the forces acting on it. This movement can be used to make or break contact with another conductive element, thus opening or closing an electrical circuit.

## 3. What are the advantages of using a cantilever switch based on electrostatic force?

One advantage of using a cantilever switch based on electrostatic force is its small size and low power consumption. These switches are also highly sensitive and can be easily controlled, making them ideal for use in electronic devices. Additionally, they have a long lifespan and are capable of operating in harsh environments.

## 4. What are some common applications of cantilever switches based on electrostatic force?

Cantilever switches based on electrostatic force have a wide range of applications in electronic devices. They are commonly used in sensors, actuators, and microelectromechanical systems (MEMS). They can also be found in touch screens, accelerometers, and inkjet printers.

## 5. How do I choose the right cantilever switch based on electrostatic force for my application?

When choosing a cantilever switch based on electrostatic force, it is important to consider factors such as the required sensitivity, voltage and current requirements, and environmental conditions. It is also important to ensure that the switch is compatible with the other components in your circuit. Consulting with a specialist or conducting thorough research can help ensure that you choose the best switch for your specific application.

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