786 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 « 



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lever points on the treated surface. The electrical characteristics of a 

 beryllium copper point, operating as transistor collector on the treated 

 surface, could then be investigated. An auxiliary etched tungsten point 

 doubled as a potential probe and as an emitter. A switching arrangement 

 allowed oscilloscope presentation of the h-Vc collector family and the 

 alpha-emitter current sweep, measurement of the emitter floating poten- 

 tial on a high impedance VTVM, and determination of other transistor 

 parameters for any desired position of the emitter point. 



Phosphor bronze collector points were not used since it was found that, 

 on certain chemically etched surfaces the mere application of a negative 

 bias of 15-40 volts for a few seconds sometimes is sufficient to cause elec- 

 trical forming of the point in the sense that Ico and average a are in- 

 creased by an appreciable amount. 



The beryllium copper points were carefully cleaned to prevent con- 

 tamination by donor elements. Their cleanHness was then tested by 

 other methods described in Section 3.3.6. 



With this arrangement, most of the electrical properties of a given 

 manipulator unit could be inspected during the time the unit ''survived." 

 These electrical measurements were made in room air (R. H. between 

 20 and 30 per cent), although provision was made for directing a con- 

 tinuous stream of dry nitrogen at the points and surrounding surface. 



3.3 Experimental Results 



3.3.1 Unformed Transistors on Superoxol Etched* Surfaces 



A striking difference was observed in the electrical characteristics of 

 unformed collector points on the \'arious n-germanium surfaces ex- 

 amined. In particular, surprisingly large values of 7c.(0, —10) and 

 /c(6, —5), (the latter taken as a measure of average a), were encountered 

 on the superoxol etched surface subsequently "soaked" for about 10 

 minutes with 24 per cent HF. At these locations the unformed transis- 

 tor action was quite similar to that observed with a conventional phos- 

 phor bronze point formed on a freshly etched surface. 



These large values were found only in specific locations on the treated 

 surface, there being a random fluctuation of 7,(0 —10) and /c(6, —5) 

 with location of the points on the surface. However, no such large values 

 of these parameters were found (together) on surfaces freshly etched in 

 superoxol. The a as a function of emitter current for the unformed points 

 (2.5 mil spacing) on a superoxol etched surface, before (Curve I) and 

 after (Curve II) HF treatment is shown in Fig. 10. Comparison with 



One part 30 por cent H2O2 , one part 48 per cent HF and four parts water. 



