909 physicist William Eccles discovered the crystal diode oscillator.[4] Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in 1925, which was intended to be a solid-state replacement for the triode.[5][6] Lilienfeld also filed identical patents in the United States in 1926[7] and 1928.[8][9] However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any specific examples of a working prototype. Because the production of high-quality semiconductor materials was still decades away, Lilienfeld s solid-state amplifier ideas would not have found practical use in the 1920s and 1930s, even if such a device had been built.[10] In 1934, German inventor Oskar Heil patented a similar device in Europe.[11]