JPS5778181A - Semiconductor variable capacity element - Google Patents

Abstract

PURPOSE:To obtain an element having small size and large maximum capacity by forming the first impurity region not depleted nor inverted by the charge of a floating electrode and the second impurity region depleted and inverted on the surface of a semiconductor substrate under a buried floating electrode in an insulating film. CONSTITUTION:An insulating oxidized film 9 is covered on a semiconductor substrate 8, an externally insulated floating electrode 10 is formed, a p type diffused layer 11 is faced with a part of the electrode 10, and a capacitive electrode 12 is mounted. A p type diffused layer 13 is formed on the surface of a substrate 8 faced with the electrode 12, and an n type diffused layer 14 to become capacitive variable terminal is formed therein. In this structure, the thickness of the oxidized film 33 made of the film 9 disposed between the electrodes 10 and 14 is set at tox 2 of approx. 200Angstrom , and the thickness of the oxidized film 32 between the surface of the substrate 8 and the floating electrode 10 is similarly set to tox 1 similarly to the thickness of tox 2. In this mannr, the thickness of the oxidized film 33 is sufficiently reduced to different depleting conditions between the layer 11 and the surface of the substrate 8, thereby obtaining a capacity value larger than the charge of the electrode 10.