2 BELL SYSTEM TECHNICAL JOURNAL 



At that time the improvement in sensitivity of microwave receivers employ- 

 ing crystal rectiliers in the frequency converters was clearly recognized, as 

 were the advantages of rectifiers using silicon rather than certain well 

 known minerals as the semi-conductor. In the second period, from 1941 

 to 1942, the advent of important war uses for microwave devices stimulated 

 increased activity in both research and development. During these years 

 the pattern for the interchange of technical information on microwave 

 devices through government sponsored channels was established and was 

 continued through the entire period of the war. With the extensive inter- 

 change of information, considerable international standardization was 

 achieved. In view of the urgent equipment needs of the Armed Services 

 emphasis was placed on an early standardization of designs for production. 

 This resulted in the first of the modern series of rectifiers, namely, the 

 ceramic cartridge design later coded through the Radio Manufacturers 

 Association as type 1N21. In the third period, from 1942 to the present 

 time, process and design advances accruing from intensive research and 

 development made possible the coding and manufacture of an extensive 

 series of rectifiers all markedly superior to the original 1N21 unit. 



It is the purpose of this paper to review the work done in Bell Telephone 

 Laboratories on sihcon point contact rectifiers during the three periods 

 mentioned above, and to discuss briefly typical properties of the rectifiers, 

 several of the more important applications and the production history. 



Crystal Rectifiers in the Early Microwave Research 



The technical need for the modern crystal rectifier arose in research on 

 ultra-high frequency communications techniques. Here as the frontier 

 of the technically useful portion of the radio spectrum was steadily advanced 

 into the microwave region, certain limitations in conventional vacuum 

 tube detectors assumed increasing importance. Fundamentally, these 

 limitations resulted from the large interelectrode capacitance and the 

 finite time of transit of electrons between cathode and anode within the 

 tubes. At the microwave frequencies (3000 megacycles and higher), they 

 became of first importance. As transit time effects are virtually absent 

 in point contact rectifiers, and since the capacitance is minute, it was logical 

 that the utility of these devices should again be explored for laboratory use. 



The design of the point contact rectifiers used in these researches was 

 dictated largely, of course, by the needs of the laboratory. Frequently 

 the rectifier housing formed an integral part of the electrical circuit design 

 while other structures took the form of a replaceable resistor-like cartridge. 

 A variety of structures, including the modern types, arranged in chrono- 

 logical sequence, are shown in the photograph, Fig. 1. In general, the 



