Johnson's figure of merit
Johnson's figure of merit is a measure of suitability of a semiconductor material for high frequency power transistor applications and requirements. More specifically, it is the product of the charge carrier saturation velocity in the material and the electric breakdown field under same conditions, first proposed by Edward O. Johnson of RCA in 1965.[1]
Note that this figure of merit (FoM) is applicable to both field-effect transistors (FETs), and with proper interpretation of the parameters, also to bipolar junction transistors (BJTs).
Example materials
| Material | Saturation velocity x104 m/s | VBreakdown MV/cm | JFM Si=1.0 | Notes/refs |
|---|---|---|---|---|
| Silicon | 1.0 | 0.3 | 1.0 | [2] |
| GaAs | 1.5 | 0.4 | 2.7 | [2] |
| SiC | 2.0 | 3.5 | 20 | [2] |
| InP | 0.67 | 0.5 | 0.33 | [2] |
| GaN | 2.5 | 3.3 | 27.5 | [2] |
JFM figures vary wildly between sources - see external links and talk page.
External links
- Gallium Nitride as an Electromechanical Material. R-Z. IEEE 2014 Table IV (p 5) lists JFM (relative to Si) : Si=1, GaAs=2.7, SiC=20, InP=0.33, GaN=27.5, also shows Vsat and Ebreakdown.
- Why diamond? gives very different figures (but no refs) :
Si GaAs GaN SiC diamond JFM 1 11 790 410 5800
References
- "Physical limitations on frequency and power parameters of transistors," RCA Review, vol. 26, pp. 163-177, June 1965.
- Gallium Nitride as an Electromechanical Material. R-Z. IEEE 2014 Table IV (p 5)
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