COMS Technology

COMS technology

n type MOS(NMOS) The structure of triode is shown in the figure , The drawing is not drawn to actual scale . The substrate of the triode is doped and becomes p Silicon wafer of type a semiconductor material .NMOS The thickness of the substrate is much thicker than other triodes . There are two regions on each triode , Be mixed with a lot of impurities , Become n Type semiconductor region . These two regions form the source and drain of the triode respectively . actually , The source and drain can be interchanged , But no matter how interchangeable , The source to drain voltage is usually positive . There are respective metal connection points on the source and drain . polysilicon (polysilicon) The grid and other areas of the triode are isolated by silicon dioxide insulation . The original , The grid also has metal connection points ;MOS The name is also derived from the structure of metal oxide semiconductor triode .

When the grid voltage is the same as the source , The source and drain are insulated . As the grid voltage rises , Grid - oxide -p The three layers of A-type semiconductor substrate are overlapped ( Sandwich ) The effect is equivalent to that of a dry capacitor , Therefore, negative charges accumulate on the surface of semiconductors . When the gradually increasing negative charge reaches the switching threshold , Form immediately between the source and drain n Channel of type silicon . This channel connects the source and drain . therefore ,NMOS Triode can be used as a switch , When NMOS When the triode grid voltage is low , The switch is off ; When the grid voltage is high , The switch is on .
stay n Two doped silicon wafers are fabricated on the substrate p Type area : Source and drain areas , It can form p type MOS( namely PMOS) The transistor . therefore , When PMOS When the grid voltage of the triode is low , The triode is on ; When the grid voltage is high , The triode is disconnected .