Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Thickness of dielectric towards capacitance?

Status
Not open for further replies.

IvanTheTerrible

Junior Member level 1
Joined
Oct 3, 2009
Messages
18
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,398
What has the thickness of a dielectric do towards capacitance?
 

Please provide some context/info of any sort. Are you asking about thickness in stripline, microstrip, coax, twin line, something else, or what?
 

Actually I was reading about MOSFET capacitance, the gate to body of a MOSFET basically act as plates for a capacitor. During certain operating regions, a depletion region will be formed under the gate, and it can be viewed as the thickness of the dielectric of the capacitor has decreased, and so will the capacitance.

That I don't get it. How does the thickness of a dielectric relates to capacitance?
 

Hello
Ivan the Terrible
The dielectric thickness controls the capacitance
as the capacitance of a capacitor is inversely proportional to the thickness. and unlike you mentioned if the thickness decreases the capacitance increases.
 
What you should have read was, as the depletion layer is formed beneath the gate oxide of the mosfet, the depletion layer (devoid of mobile charges and therefore essentially an insulator) increases the thickness of the effective dielectric (gate oxide plus the depletion zone) and decreases the capacitance.
This depletion zone continues to increase in thickness until and inversion layer forms in the channel imediately below the gate oxide. At this point, there is mobile charges immediately below the gate oxide and so the capacitance increases back to the original value εA/Tox
 

The blue curve in this figure shows how the capacitance varies bfore inversion and after inversion.
**broken link removed**
Before inversion it decreases with thickness and afte inversion , due to the mobile carriers availble, the capacitance inreases.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top