SJ Electric Field Profiles

Figure 6.5 shows the simulation plots of SJ structure with W = 5 ^m and L = 15 fzm at different positive Vds bias when Vgs = 0 V produced by MEDICI.

Table 6.1. a values between Ex,max and ?crjt at different ratios of W/L.

1.5 x 1015

  • 19.5
  • 3.16 x 1015

1.126 x 105 1.3 0.356

1.430 X 105 0.975 0.453

2.065 x 105 0.39 0.654

3.2 x 1015

  • 10
  • 3.48 x 1015

1.956 x 105 0.667 0.562

2.158 x 105 0.5 0.620

2.329 x 105 0.2 0.669

1.27 x 1016 7.1 x 1015

3 5 4.13 xlO15 3.84 xlO15

2.773 x 105 2.546 x 105 0.2 0.333 0.671 0.663

2.775 x 105 2.577 x 105 0.15 0.25 0.672 0.671

2.775 x 105 2.585 x 105 0.06 0.1 0.672 0.673

4.47 x 1016

  • 1
  • 4.84 x 1015

3.256 x 105 0.067 0.673

3.256 x 105 0.05 0.673

3.256 x 105 0.02 0.673

9.8 x 1016

  • 0.5
  • 5.33 x 1015

3.569 x 105 0.033 0.670

3.569 x 105 0.025 0.670

3.569 x 105 0.01 0.670

N (cm 3)

W (/j.m) Ec (V/cm)

L = 15/xm Ex,max (V/cm) W/L

иАЁх,тга/Ec

L = 20 /xm Ex,max (V/cm) W/L

a = Ex, max/Ec

L = 50 /ли Ex,max (V/cm) W/L

а — Ex,max! Ec

Relationship between E,max/Ec and W/L for SJ structure

Fig. 6.3. Relationship between Ex,max/Ec and W/L for SJ structure.

R,sp vs Vb performance merit of ideal unipolar silicon limit and SJ limits at W = 5 im, 0.5 im, and 0.05 im

Fig. 6.4. Ron,sp vs Vbr performance merit of ideal unipolar silicon limit and SJ limits at W = 5 im, 0.5 im, and 0.05 im.

Equipotential lines within SJ structure at different Eds bias before breakdown

Fig. 6.5. Equipotential lines within SJ structure at different Eds bias before breakdown.

Vbr is simulated to be 261V for this structure. The doping concentrations NA and Nd for p- and n-column in the structure are exactly equal to get the ideal result. However, in the practical fabrication, perfect match of NA = ND is difficult to achieve. The analysis of charge imbalance will be discussed in the later part of this chapter. When VDS = 0 (see Fig. 6.5(a)), the depletion region that results from built-in potential between p-n columns is very small. The built-in potential (Vbi) is approximated by

From Eq. (6.14) we know that in the case of NA = ND = 7 x 1015 cm-3, the built-in depletion width (Wbi) is about 0.5 fim. After VDS > 0, the depletion region starts to extend. It is observed in Figs. 6.5(b)-(d) that the depletion region first merges on the top part of the drift region at a small bias, then moves down with the increase of the bias.

At the breakdown, the entire drift region is fully depleted as shown in Fig. 6.6. The distribution of equipotential lines (the parallel curves shown in Fig. 6.6(a)) is nearly uniform within the drift region. The E-field vector plots in Fig. 6.6(b) represents that electric field crowds obviously at the p-n column interface, especially at the top and bottom regions. Along the vertical direction at the center of the n-drift region, only vertical electric field is found. The above simulation result verifies the electric field profile as shown in Fig. 6.2.

(a) Equipotential lines at 10 V interval, impact ionization representation and (b) E-field vector plots for SJ structure at breakdown

Fig. 6.6. (a) Equipotential lines at 10 V interval, impact ionization representation and (b) E-field vector plots for SJ structure at breakdown.

As shown in Fig. 6.7(a), when increasing Ads, the vertical electric field profiles of SJ structure at the center of n-column (x = 5 p.m) start to transform from a triangle shape as that in the conventional case to a trapezium-like distribution. The electric field at p-n interface (x = 2.5 p.m) as shown in Fig. 6.7(b) is almost in the same shape at any bias but different in magnitude as determined by the applied bias.

 
Source
< Prev   CONTENTS   Source   Next >