CATHODE SPUTTERING 



285 



as blisters, peeling, and pin Iioles probably due largely to electrolytic 

 corrosion. The substitution of the sputtering process has practically 

 eliminated such defects. Some additional advantage over electrolytic 

 plating is that a thinner continuous film can be deposited, making it 

 possible to stretch the diaphragm to a higher natural frequency with 

 less tension. This decrease in tension has resulted in a smaller fre- 

 quency loss due to fatigue. The introduction of the sputtering process 

 has, therefore, not only improved the quality of the microphone, but 

 lengthened its life. 





v..^ 



I GRANULAR^ 

 CARBON 



■-DIAPHRAGM j ( DAMPING 



INITIAL I FINAL BAKELIZED PLATE GROOVE 



STRETCHING-J STRETCHING PAPER DIAPHRAGM 



RING RING DAMPING RINGS 



Fig. 1 — Cross-sectional view of the two-carbon-chamber, stretched- 

 diaphragm microphone. 



Equipment and Method 



In order to apply a satisfactory gold electrode surface to the dura- 

 lumin diaphragm by cathode sputtering commercially, it was neces- 

 sary to develop a special cleaning process for the diaphragms and 

 suitable equipment with multiple sputtering electrodes. 



To insure proper continuity and adherence of the gold to the dura- 

 lumin, the glossy roll finish on the duralumin is broken up by means of 

 a brass wire scratch brush to give a matte surface. The diaphragms 

 are then scrubbed in acetone, rinsed in ether, and rubbed dry with 

 filter paper to remove all traces of oil or grease. Great care is then 



