AN2386 datasheet(17/30 Pages) STMICROELECTRONICS

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AN2386

Some considerations on VTH and TVTC equations and real examples

17/30

As shown in Figure 6. and Figure 7., the data simulated and measured are quite close to

each other. In this case, for DEVICE1, the threshold voltage is around 3.2V (standard VTH)

and TVTC is around 3mV/K at ambient temperature. In the next Figure 8. the contribution of

each component of (Equation 42) is highlighted.

Figure 8.

Weight of single term of (Equation 42) on TVTC at different temperatures

In the graph above it is possible see that at a low temperature, the higher weight in the

TVTC formula is established by the parameters

Φms/T and 2ΦF/T. The first term is negative

and makes TVTC negative, while the second term in positive and makes TVTC positive.

When the temperature increases, TVTC increases in absolute value because even if

Φms/T

decreases, 2

ΦF/T also decreases and in particular, the weight of ∂Vox/ ∂T increases too.

Another real example of threshold voltage and TVTC compared to the theoretical model

implemented is shown below. The low voltage power MOSFET takes into consideration a

device of 55V of breakdown voltage and 6.5mOhm of on resistance (production line

DEVICE1). This device has a gate doping concentration (Ng) equal to 1e+20cm

-3, a

substrate doping concentration peak in the channel (Na) equal to 1e+17cm

-3, an oxide

thickness of 350Å and a channel length of 0.35µm. The following tab summarizes the main

simulated electrical parameter function of T (T range is 250-400K) and then a graphs

highlights the DEVICE2 measured and simulated data.

Table 2.

Main electrical parameter simulated by DEVICE2

Tni

Φms

∂ms/∂T

Φms/T

ΦF

∂ΦF/∂T

ΦF/T

VOX

∂VOX/∂TVth

∂Vth/∂T

250

9.67E+13 -1.043 0.000927

-0.00417 0.447

-0.00076 0.0018 1.76

-0.0015

1.61

-0.0021

255

1.73E+14 -1.038 0.000932

-0.00407 0.443

-0.00076 0.0017 1.75

-0.0015

1.60

-0.0021

260

3.02E+14 -1.033 0.000937

-0.00397 0.439

-0.00077 0.0017 1.74

-0.0015

1.59

-0.0021

265

5.18E+14 -1.029 0.000942

-0.00388 0.436

-0.00077 0.0016 1.74

-0.0015

1.58

-0.0021

270

8.70E+14 -1.024 0.000947

-0.00379 0.432

-0.00077 0.0016 1.73

-0.0015

1.57

-0.0021

275

1.43E+15 -1.019 0.000952

-0.00371 0.428

-0.00077 0.0016 1.72

-0.0016

1.56

-0.0022

280

2.33E+15 -1.015 0.000957

-0.00362 0.424

-0.00078 0.0015 1.71

-0.0016

1.55

-0.0022

285

3.71E+15 -1.010 0.000961

-0.00354 0.420

-0.00078 0.0015 1.71

-0.0016

1.54

-0.0022

290

5.82E+15 -1.005 0.000966

-0.00347 0.416

-0.00078 0.0014 1.70

-0.0016

1.53

-0.0022

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