Module Four: Field-Effect Transistors

Vocabulary flashcards covering the characteristics, operational modes, and mathematical relationships of Junction Field-Effect Transistors (JFETs) and Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs).

Field-Effect Transistor (FET)

A voltage-controlled device, sometimes called a unipolar transistor, constructed using only one type of doped semiconductor material where current flow is controlled by an electric field.

Source

One of the two ends of the semiconductor material in a FET from which current (majority carriers) flows.

Drain

One of the two ends of the semiconductor material in a FET to which current (majority carriers) flows.

Gate

The terminal where the control voltage is applied to manage the flow of current between the source and the drain.

Substrate (body)

The base material that supports all terminals of a Field-Effect Transistor.

Input Impedance of FET

A very high value of several mega ohms (MQ) that results in very little current running through the device and minimal loading on original circuit elements.

Junction FET (JFET)

A type of FET made with either N-type or P-type material as the main channel, with a gate made of the opposite type of material diffused into a strip on each side.

Insulated FET (IFET)

Another name for the Metal-Oxide Semiconductor FET (MOSFET), characterized by an insulated gate.

Pinch-off condition

The state where the depletion region completely closes the channel, causing the channel resistance to rise to infinity.

Pinch-off voltage ($V_P$)

The specific voltage $V_{DS}$ at which the depletion region closes the channel and the drain current reaches a saturation level.

$$I_{DSS}$$

The maximum drain current saturation level obtained for an N-channel JFET when the conditions $V_{GS} = 0V$ and $V_{DS} > V_P$ are met.

Voltage Controlled Resistor Resistance ($r_d$)

The resistance between the drain and the source defined by the slope of the current-voltage curve before pinch-off, calculated as $r_d = \frac{r_o}{(1 - \frac{V_{GS}}{V_P})^2}$.

Breakdown region

A point at high levels of $V_{DS}$ where the current curves suddenly rise up unbounded.

Transfer Characteristics of JFET

The non-linear relationship between output current $I_D$ and control voltage $V_{GS}$, expressed as $I_D = I_{DSS} (1 - \frac{V_{GS}}{V_P})^2$.

Dielectric

A thin silicon dioxide ($SiO_2$) layer used in MOSFETs as an insulator to set up an opposing electric field when an external field is applied.

Depletion mode

A MOSFET operation where applying a gate voltage reduces the drain current ($I_D$) due to the recombination of charge carriers.

Enhancement mode

A MOSFET operation where applying a gate voltage attracts more charge carriers from the substrate, causing the drain current ($I_D$) to increase rapidly.

Enhanced N-Channel MOSFET

A type of MOSFET where no N-channel exists at $V_{GS} = 0V$; the channel is only created when a positive voltage is applied to the gate.

Threshold voltage ($V_T$)

The minimum value of $V_{GS}$ required to induce a channel and support the flow of reasonable drain current in an enhanced MOSFET.

$$V_{DS(sat)}$$

The drain-source saturation voltage in an enhanced MOSFET, related to threshold voltage by the formula $V_{DS(sat)} = V_{GS} - V_T$.

Enhanced MOSFET Drain Current Formula

The equation governing drain current above the threshold voltage: $I_D = k(V_{GS} - V_T)^2$, where $k$ is a constant based on device construction.

Field-Effect Transistor (FET)

A voltage-controlled device, sometimes called a unipolar transistor, constructed using only one type of doped semiconductor material where current flow is controlled by an electric field.

Source

One of the two ends of the semiconductor material in a FET from which current (majority carriers) flows.

Drain

One of the two ends of the semiconductor material in a FET to which current (majority carriers) flows.

Gate

The terminal where the control voltage is applied to manage the flow of current between the source and the drain.

Substrate (body)

The base material that supports all terminals of a Field-Effect Transistor.

Input Impedance of FET

A very high value of several mega ohms (MQ) that results in very little current running through the device and minimal loading on original circuit elements.

Junction FET (JFET)

A type of FET made with either N-type or P-type material as the main channel, with a gate made of the opposite type of material diffused into a strip on each side.

Insulated FET (IFET)

Another name for the Metal-Oxide Semiconductor FET (MOSFET), characterized by an insulated gate.

Pinch-off condition

The state where the depletion region completely closes the channel, causing the channel resistance to rise to infinity.

Pinch-off voltage ($V_P$)

The specific voltage $V_{DS}$ at which the depletion region closes the channel and the drain current reaches a saturation level.

$$I_{DSS}$$

The maximum drain current saturation level obtained for an N-channel JFET when the conditions $V_{GS} = 0V$ and V_{DS} > V_P are met.

Voltage Controlled Resistor Resistance ($r_d$)

The resistance between the drain and the source defined by the slope of the current-voltage curve before pinch-off, calculated as $r_d = \frac{r_o}{(1 - \frac{V_{GS}}{V_P})^2}$.

Breakdown region

A point at high levels of $V_{DS}$ where the current curves suddenly rise up unbounded.

Transfer Characteristics of JFET

The non-linear relationship between output current $I_D$ and control voltage $V_{GS}$, expressed as $I_D = I_{DSS} (1 - \frac{V_{GS}}{V_P})^2$.

Dielectric

A thin silicon dioxide ($SiO_2$) layer used in MOSFETs as an insulator to set up an opposing electric field when an external field is applied.

Depletion mode

A MOSFET operation where applying a gate voltage reduces the drain current ($I_D$) due to the recombination of charge carriers.

Enhancement mode

A MOSFET operation where applying a gate voltage attracts more charge carriers from the substrate, causing the drain current ($I_D$) to increase rapidly.

Enhanced N-Channel MOSFET

A type of MOSFET where no N-channel exists at $V_{GS} = 0V$; the channel is only created when a positive voltage is applied to the gate.

Threshold voltage ($V_T$)

The minimum value of $V_{GS}$ required to induce a channel and support the flow of reasonable drain current in an enhanced MOSFET.

$$V_{DS(sat)}$$

The drain-source saturation voltage in an enhanced MOSFET, related to threshold voltage by the formula $V_{DS(sat)} = V_{GS} - V_T$.

Enhanced MOSFET Drain Current Formula

The equation governing drain current above the threshold voltage: $I_D = k(V_{GS} - V_T)^2$, where $k$ is a constant based on device construction.