How can I experimentally calculate threshold voltage in MOS transistor?_How can I experimentally calculate threshold voltage in MOS transistor?
How can I experimentally calculate threshold voltage in MOS transistor?
By experimentally you mean in silicon or by simulation?
Threshold voltage for measurement purpose can be defined in many ways. One common measure is: Threshold voltage is the Gate-Source voltage at which the Ids (drain-source current) for diode connected MOS is 100nA. There are other standard methods such as: maximum slope method, three point method etc.
You may find a good summary in following thesis (see chapter 3 specifically):
http://www.jeroencroon.nl/Jeroen_Croon_jun04.pdf
This paper should exactly answer your question. It shows that there are a lot of ways to do and give a feeling for the differences:
http://www.sciencedirect.com/science/article/pii/S0026271402000276
Surely there are many ways of experimentally measuring the Vth of a MOSFET. However one of the most used and practicable is the following:
Just collect an Id vs Vgs curve at a fixed LOW Vds voltage (say 0.5 V for example) . You obtain a characteristic Id which is flat and quasi-zero up to a certain value range where it promptly start increasing in a quasi-linear way and appears to reach linearity after few more volts of the gate ramp. Then carry on an extrapolation to zero-current of the linearly rising region of the curve and the abscissa you get is a good valuation of the threshold voltage. The larger the expected Vth (say around 2 V or more) , the better the accuracy of the method.
See also:
Ortiz-Conde, Adelmo, Francisco J. García-Sánchez, Juan Muci, Alberto Terán Barrios, Juin J. Liou, and Ching-Sung Ho. "Revisiting MOSFET threshold voltage extraction methods." Microelectronics Reliability 53, no. 1 (2013): 90-104.
https://doi.org/10.1016/j.microrel.2012.09.015
Article Revisiting MOSFET threshold voltage extraction methods
The above paper should exactly answer your question. It shows that there are a lot of ways to do and give a feeling for the differences.
Good Luck
Conference Paper Threshold voltage extraction methods for MOS transistors
You can follow the above journal as a reference to your question.
What you need to determine the the threshold voltage is to apply the equation of the drain current as a function of gate to source voltage VGS at VDS saturation region. The saturation region is defined by VDSsat=> VGS-Vth.
It is called the transfer curve at drain current saturation. Such curve would follow the relation:
IDS= beta( VGS- Vth)^2/2 where beta is the transconductance parameter.
Then by drawing sqroot of IDS versus VGS one get a staight line when extraplated to IDS=0 it cuts the VGS axes in the threshold voltage Vth.
For more information about the theory of the FET please refer to the book:Book Electronic Devices
Best wishes
You may also take a look at:
Ortiz-Conde A, García-Sánchez FJ, Muci J, Barrios AT, Liou JJ, Ho CS. Revisiting MOSFET threshold voltage extraction methods. Microelectronics Reliability. 2013 Jan 1;53(1):90-104.
http://dx.doi.org/10.1016/j.microrel.2012.09.015
Yes, there are several ways to experimentally measur the Vth of a MOSFET and Dr. Francisco Javier García-Sánchez gave you a good reference. However what I want to say is that: after many years of working with MOSFETs in industry and academia still I believe the most effective and practicable is that you measure the Vgs at drain current of 40 nA*Wg/Lg at very low Vd (< 0.1 V) for linear Vth and at high Vd (> 1 V) for saturation Vth. This means:
Id (Vgs=Vth)=40 nA*Wg/Lg
With this approach you can see the SCEs very well.
Please read my book ( Conference Paper The American University Laboratories For Electrical Engineering Part 1
)You will find a nice way to get the I-V curve on the oscilloscop. Vp is very clear on this curve.
Response to the linear input voltage (ramp input), while the drain and source terminals are connected to supply and ground potentials is the simplest way. Beginning of the square I-V characteristic at the end of exponential waveform clarifies the boundary of sub-threshold and saturation region.
Hi,
can anyone tell me why we need the square root of Ids to find the threshold voltage?
Thank you.
Sara Arshad
We extract the threshold voltage (Vth) of a MODFET from the input I-V characteristic (drain current versus gate-source voltage). If you extract the Vth in the saturation region, drain current is a parabola function of (Vgs-Vth). But in the linear region, in which often the Vth is extracted, there is a linear relation.
You might want to take a look at:
Revisiting MOSFET threshold voltage extraction methods (Introductory Invited Article), A. Ortiz-Conde, F.J. García-Sánchez, J. Muci, A. Terán Barrios, J. J. Liou, Ching-Sung Ho, Microelectronics Reliability, vol. 53, no. 1, pp. 90-104, Jan. 2013. http://dx.doi.org/10.1016/j.microrel.2012.09.015
Are the above suggested methods also applicable for measuring threshold voltage of finfet ?
Just find the library or datasheet. Read and search it for the threshold voltage. Your answer is there. But in a more complicated path, consider I-V in the saturation region. Id=0.5 un * Cox * (W/L) * (Vgs-Vth)^2. So by knowing all parameters Vth can be found.
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators