SEMICONDUCTOR DEVICE
A semiconductor device 1 includes MOS transistors 10 and 70 and a MOS varactor 20 . The transistors 10 and 70 and the varactor 20 are formed in the same semiconductor substrate 30 . The gate insulating films 15 and 75 of the transistors 10 and 70 are the thinnest gate insulating films in the gate insulating films of the transistor formed in the semiconductor substrate 30 . The thickness of the gate insulating film 25 of the varactor 20 is larger than the thickness of the gate insulating films 15 and 75.
1 . A semiconductor device, comprising:
a metal-oxide-semiconductor (MOS) type transistor provided in a semiconductor substrate; and
a MOS type varactor provided in said semiconductor substrate;
wherein a gate insulating film of said varactor is thicker than the thinnest gate insulating film in gate insulating films of said transistor.
2 . The semiconductor device as set forth in claim 1 , wherein said varactor constitutes an LC resonance-type voltage controlled oscillator.
3 . The semiconductor device as set forth in claim 2 , wherein said gate insulating film of said varactor is thicker than a gate insulating film of a transistor that constitutes said voltage controlled oscillator.
4 . The semiconductor device as set forth in claim 1 , wherein an equivalent oxide thickness of said thinnest gate insulating film of said transistor is lower than 1.5 nm.
5 . The semiconductor device as set forth in claim 1 , wherein said varactor includes a well region of a first type conductivity provided in said semiconductor substrate, a diffusion layer of said first type conductivity provided in said well region and a gate electrode provided on said semiconductor substrate through said gate insulating film.
6 . The semiconductor device as set forth in claim 5 ,
wherein said diffusion layer includes a first diffusion layer of said first type conductivity provided in one side of said gate electrode and a second diffusion layer of said first type conductivity provided in the other side of said gate electrode, and
wherein said first diffusion layer is electrically coupled to said second diffusion layer.