History of hearing aids
The development of transistors in 1948 by Bell Laboratories led to major improvements to the hearing aid. The transistor was invented by John Bardeen, Walter Brattain, and William Shockley. Transistors were created to replace vacuum tubes; they were small, required less battery power and had less distortion and heat than their predecessor. These vacuum tubes were typically hot and fragile, so the transistor was the ideal replacement.The 1952 Sonotone 1010 used a transistor stage along with vacuum tubes, to extend battery life. The size of these transistors led to developments in miniature, carbon microphones. These microphones could be mounted on various items, even eyeglasses. In 1951, Raytheon manufactured the transistor and was one of the first companies to mass-produce transistors to throughout America. Raytheon realized that their hearing aid only lasted short-term and began to sell the vacuum-tube hearing aids again along with transistor hearing aids.
Invention of the integrated circuit
In May 1952, Sidney Darlington filed a patent application in the United States for a structure with two or three transistors integrated onto a single chip in various configurations; in October 1952, Bernard Oliver filed a patent application for a method of manufacturing three electrically connected planar transistors on one semiconductor crystal. On May 21, 1953, Harwick Johnson filed a patent application for a method of forming various electronic components – transistors, resistors, lumped and distributed capacitances – on a single chip. Johnson described three ways of producing an integrated one-transistor oscillator. All of them used a narrow strip of a semiconductor with a bipolar transistor on one end and differed in the methods of producing the transistor. The strip acted as a series of resistors; the lumped capacitors were formed by fusion whereas inverse-biased p-n junctions acted as distributed capacitors. Johnson did not offer a technological procedure, and it is not known whether he produced an actual device. In 1959, a variant of his proposal was implemented and patented by Jack Kilby.