DIFFUSED y-n JUNCTION SILICON RECTIFIERS 673 



i I and all the units have dice about 0.005" thick. The medium size device 

 has a wafer 0.100" by 0.100" in area. The largest device has a element 

 0.250" by 0.250" in area. It is obvious that a range of die size could have 

 been chosen for any of these rectifiers. However, electrical and thermal 

 considerations have dictated minimum sizes and economic considera- 

 tions have suggested maximum sizes. The actual sizes are intermediate 

 in value and appear to be satisfactory for the given ratings. 



5.2 Of fundamental importance to users of these rectifiers are the for- 

 ward and reverse current — voltage characteristics. These characteris- 

 tics of the medium size iniit are shown in Fig. 7 for two temperatures, 

 25°C and 125°C, using logarithmic scales. It can be seen that in the 

 forward direction at room temperature, 25°C, more than 20 amperes 

 are conducted with a one volt drop in the rectifier. At the higher tem- 

 perature more current will be conducted for a given voltage drop. In 

 the reverse direction, this particular unit can withstand inverse voltages 

 as high as 300 volts before conducting appreciable currents (>1 ma) 

 even at 125°C. A comparison of the current-voltage characteristics for 

 the three different size units is shown in Fig. 8 where again the informa- 

 tion is plotted on logarithmic scales. This information was obtained at 

 25°C. One can observe that the reverse leakage current varies directly 

 as the area of the device and the forward voltage drop varies inversely 

 as the area. These relations are to be expected; however, the reverse 

 characteristics indicate that surface effects are probably effecting the 

 exact shape of the curves. The changes in the forward characteristics 

 can be attributed to the contacts and the internal leads of the packages. 

 The breakdown voltage can be adjusted in any size device by the proper 

 choice of starting material and therefore no significance should be placed 

 on the different breakdown voltages in Fig. 8. 



SILICON GERMANIUM SELENIUM 



Fig. 9 — Semiconductor rectifiers of different materials. 



