Surface Inversion and Threshold Voltage Calculation Surface inversion is a crucial phenomenon in MOS devices where the semiconductor material (n-type or p-ty...
Surface inversion is a crucial phenomenon in MOS devices where the semiconductor material (n-type or p-type) at the surface becomes positively or negatively charged due to the applied voltage. This can significantly impact the device's electrical properties, including its threshold voltage and conducting characteristics.
Threshold voltage:
When a negative voltage is applied to the gate terminal, the surface becomes negatively charged.
This creates a region of positive charge (holes) near the surface due to the depletion region formed by the applied voltage.
The depletion region effectively reduces the effective width of the channel, hence the threshold voltage.
Surface inversion and threshold voltage:
When a positive voltage is applied to the gate terminal, the surface becomes positively charged.
The depletion region now forms near the gate, effectively narrowing the channel width.
This reduces the effective width of the channel, causing the threshold voltage to be higher.
Examples:
Apply a negative voltage to the gate, like Vgs = -1V.
Due to the depletion region, positive charge carriers (holes) are attracted to the surface, resulting in surface inversion.
This creates a region of negative charge carriers near the surface, making the device conductive.
Apply a positive voltage to the gate, like Vgs = +1V.
The depletion region forms near the gate, creating a region of negative charge carriers (holes) near the surface.
This reduces the effective width of the channel, causing the threshold voltage to be higher.
These examples illustrate how surface inversion and threshold voltage are inversely related to the applied gate voltage. By manipulating the gate voltage, we can control the channel width and modify the device's electrical properties