P-N-I-P AND N-P-I-N JUNCTIOX THAXSISTOU TRIODKS 529 



U = ., ( 1 u-,. (9) 



Equation (9) implies (correctly) that the delay time for total current 

 passing through the depletion layer is about one-half the transit time 

 for the carriers. This results from the induction of charge on the base 

 and collector electrodes by the carriers in transit. If ^ = core is carrier 

 transit angle and Jc = e'" is the conduction current of holes entering 

 the depletion layer from the base, the total current entering the depletion 

 laver from the base can be shown to be 



which reduces for small ^ to 



It may be noted that the total current / of eciuation (3.6-2), when written 

 in the form Jmax Z in which 6 is the phase shift of the total current ^\dth 

 respect to the conduction current entering from the base, is approxi- 

 mately 0.973 Z -22.5° for ^ = 45°, 0.901 Z -45° for ip = 90°, and 

 0.636 Z -90°for<i5 = 180°. 



DESIGN COMPARISON 



Gene7-al 



Comparison of figures of merit is the best, albeit unsatisfactory, means 

 for comparative evaluation of devices. For junction transistors, one 

 non-controversial figure of merit is established — the noise figure. Tavo 

 transmission figures of merit for junction transistors are suggested at 

 the bottom of Table I. It should be pointed out that the p-n-i-p figures 

 are for theoretical design possibilities, some features of which have al- 

 ready been realized experimentally. 



The Units 



Table I gives parameters of interest for several types of transistors. 

 Structural, material, and electrical parameters for the Bell Telephone 

 Laboratories' developmental M1778 p-n-p unit are averages for large 

 numbers of units. The electrical parameters of the plated-contact tran- 

 sistor recentl}^ annoiuiced by Philco wcn-e taken from a talk by W. H. 

 Forster before the Philadelphia I.R.E., Dec. 3, 1953.^" The structural 

 and material parameters have been estimated. The p-n-i-p structures 



