Parametrischer Verstaerker

948,058. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. May 25, 1960 [June 12, 1959], No. 18458/60. Heading H3B. [Also in Division H1] A parametric amplifier includes a voltage variable capacitance unit comprising a dielectric layer contacting a semiconductor region of material with a carrier mobility of at least 100 cms.2 per v.sec. Fig. 1 shows an N-type silicon wafer 1 sandwiched between layers 2 and 3 of silicon oxide having evaporated metal layers 4 and 5 with lead wires attached. When this ONO (i.e. oxide-N-type-oxide) device is biased with layer 4 positive, a depletion layer forms at the negative silicon-oxide interface 1-3, the thickness t of which varies as (Vp)¢ where # is the resistivity of the silicon and V the bias voltage, thus providing a variable capacity in series with the capacity due to the oxide layers. If V is large enough, the depletion layer occupies the whole of the silicon layer, but there is no punch-through effect. The effect of thermally generated electron-hole pairs is discussed, whereby holes tend to accumulate at the negative interface, possibly forming an inversion layer, and electrons tend to cancel positive fixed changes in the depletion layer and possibly form an accumulation layer; this results in decreased sensitivity for the variable depletion layer capacitance. The tendency for accumulation and inversion layers to form, may be reduced by providing a leakage path through the oxide layer such as by reducing its resistivity to, say, 1012 ohm cms., or providing a thin conducting coating over the oxide-semiconductor junctions. Limiting frequencies and figure of merit are discussed. Other types of units are described with different layer arrangement. If one oxide layer is omitted, the arrangement constitutes an ON device which has less accumulation effects and the capacity variation occurs at the same frequency as the pump, instead of twice this frequency as in the ONO device. An ONPO device containing a PN junction is described wherein depletion layers occur at the PN junction with reverse bias or at the ON and PO junction with forward bias. Reference is also made to a number of ON devices mounted in series, either by a plurality of layers as described, or by having a number of coated particles or flakes bonded together, for example by using low melting point glass such as described in Specification 923,338 or 942,755 containing As and S or As and Se with Te. In this case, the glass provides the dielectric in place of th