What is the relationship between PMOS and NMOS transistors?
Click to see answer
They are complementary devices.
Click to see question
What is the relationship between PMOS and NMOS transistors?
They are complementary devices.
What happens when v_DS exceeds v_OV?
The channel depth at the drain end reduces to zero, leading to channel pinch-off.
What happens to the resistance of a MOSFET as v_GS increases above V_t?
The resistance decreases, while it is infinite for v_GS ≤ V_t.
What happens when a positive voltage is applied to the gate of an NMOS transistor?
It repels free holes from the channel region, creating a carrier-depletion region.
What happens to the voltage drop along the channel when v_DS is applied in a MOSFET?
It varies linearly, with an average value at the midpoint.
What happens to the channel shape as v_DS is increased?
The channel becomes more tapered and its resistance increases.
What happens when the magnitude of the negative gate-source voltage exceeds the threshold voltage in a PMOS transistor?
A p-channel is established.
What is the gate current (i_G) in a MOSFET?
i_G = 0.
What is the significance of L_min in MOSFET fabrication?
It represents the minimum channel length for a given fabrication process, which is continually reduced with technological advancements.
What are the heavily doped regions in the n-channel enhancement-type MOSFET called?
n+ source and n+ drain regions.
What types of circuits can be implemented using MOSFET technology?
Both analog circuits like amplifiers and digital circuits.
What does the voltage between two terminals of a MOSFET control?
The current that flows through the third terminal.
How does the channel depth at the source end relate to v_OV?
It is proportional to v_OV.
How does the i_D - v_DS curve behave as the channel resistance increases?
It does not continue as a straight line but bends.
What is the voltage at which saturation occurs in a MOSFET?
v_DS sat, denoted as v_OV.
What type of MOSFET is the most widely used?
Enhancement-type MOSFET.
What was the state-of-the-art channel length in commercially available MOS technology in 2019?
14 nm.
How does oxide thickness (t_ox) relate to channel length (L_min)?
Oxide thickness scales down with L_min; for example, t_ox is 2.7 nm for 0.13-μm technology and 2.2 nm for 65-nm technology.
What is the typical range for the length (L) of an n-channel enhancement-type MOSFET?
20 nm to 1 μm.
What is the thickness range of the oxide layer (tox) in an n-channel enhancement-type MOSFET?
1 to 10 nm.
What does the term 'metal-oxide-semiconductor FET' refer to?
It refers to the physical structure of the MOSFET.
What occurs when zero voltage is applied to the gate of a MOSFET?
Two back-to-back diodes are formed, preventing current conduction from drain to source.
What is the induced n region in an NMOS transistor responsible for?
It forms a channel for current flow from drain to source.
What is the typical range for the threshold voltage (Vt) during device fabrication?
0.3 V to 1.0 V.
What is required for a MOSFET to conduct?
A channel has to be induced.
How is the drain current (iD) calculated in a MOSFET?
By multiplying the charge per unit channel length by the electron drift velocity.
How is the transconductance parameter for a PMOS device defined?
It is defined as the product of hole mobility and the aspect ratio W/L.
What is the process transconductance parameter?
The product of electron mobility (μn) and oxide capacitance (Cox).
Why is CMOS technology widely used in integrated circuits?
It enables powerful circuit configurations and has virtually replaced NMOS designs.
What does the overdrive voltage (v_OV) determine in a MOSFET?
It directly determines the magnitude of electron charge in the channel and is an important circuit-design parameter.
What is the triode region in MOSFET operation?
It refers to the region of operation obtained with a continuous (non-pinched-off) channel.
What is the effect of connecting the body terminal to the source terminal in a MOSFET?
It effectively cuts off the two pn junctions.
What type of MOSFET is described in the text?
p-Channel enhancement-type MOSFET.
What voltage condition induces a p-channel in a p-channel MOSFET?
A negative voltage vGS of magnitude greater than |Vtp|.
What is the primary focus of this chapter?
The metal-oxide-semiconductor field-effect transistor (MOSFET).
What is the relationship between the charge in the tapered channel and the channel cross-sectional area?
The charge is proportional to the channel cross-sectional area.
What does the (W/L) ratio represent in MOSFET design?
It is a dimensionless quantity determined by the device designer to achieve desired i-v characteristics.
How does the voltage between the gate and points along the channel change as you move from source to drain?
It decreases from v_GS at the source end to v_GD at the drain end.
How does the aspect ratio (W/L) affect channel conductance?
It is proportional to the channel width W and inversely proportional to the channel length L.
What happens to the current and voltage drop across the channel in saturation mode?
Both the current through the channel and the voltage drop across it remain constant.
What effect does doubling the channel width have on the drain current (iD)?
It increases the drain current.
What is the main focus of Chapter 5?
MOS Field-Effect Transistors (MOSFETs).
How does the structure of a p-channel MOSFET differ from that of an NMOS device?
The substrate is n-type, and the source and drain regions are p+ type, reversing the polarity.
What condition must be met for the channel at the drain end of a MOSFET to have a finite depth?
The voltage between the gate and the drain, v_GD, must exceed V_t.
What is the relationship between the electron drift velocity and the mobility of electrons?
The drift velocity is given by the mobility of the electrons at the surface of the channel, μn.
What carries the current in a p-channel MOSFET?
Holes carry the current.
What happens to the channel depth as v_DS is increased while v_GS is held constant?
The channel takes a tapered shape, being deepest at the source end and shallowest at the drain end.
What is CMOS technology?
A technology that allows the fabrication of both NMOS and PMOS transistors on the same chip.
What is the relationship between MOSFETs and amplifier design?
MOSFETs are foundational for amplifier design, as they can act as controlled sources.
How does a MOSFET behave when v_DS is kept small?
It behaves as a linear resistance (r_DS) controlled by the gate voltage (v_GS).
In a given process technology, what parameters are needed to calculate C ox?
L min, t ox, μ n, and V t.
What is the effect of doubling the drain-to-source voltage on the drain current (iD)?
It increases the drain current.
What condition must be met for the channel to exist at the drain end of a MOSFET?
v_GD must be greater than V_t.
What voltage is applied to the gate to induce a channel for current flow in a PMOS transistor?
A negative voltage is applied between gate and source.
What is the relationship between the currents at the source and drain terminals of a MOSFET?
The current leaving the source (i_S) is equal to the current entering the drain (i_D).
Does channel pinch-off mean channel blockage?
No, current continues to flow through the pinched-off channel.
What is the substrate material used in the n-channel enhancement-type MOSFET?
p-type single-crystal silicon wafer.
What is the purpose of the silicon dioxide (SiO2) layer in the MOSFET structure?
It acts as an excellent electrical insulator.
What parameters do the graphs in Fig. 5.4 depend on?
They depend on v_OV and k_n, even though v_GS is used as the parameter.
What are the three terminals of a MOSFET?
Gate (G), Source (S), and Drain (D).
What will you learn about current-voltage characteristics in this chapter?
The equations that describe these characteristics.
What is the effect of the positive gate voltage on the n+ source and drain regions?
It attracts electrons into the channel region, forming an n region.
What concept related to microelectronics is covered in this chapter?
Moore's Law and its impact over the past 50 years.
What causes the channel electrons in a MOSFET to drift toward the drain?
The electric field created in the channel.
What occurs to the drain current when v_DS is increased beyond v_OV?
The drain current saturates and remains constant.
Why has the MOSFET become the most widely used electronic device?
It can be made small, is simpler to manufacture, and requires less power.
What happens to v_GD at the drain end when the MOSFET enters saturation mode?
v_GD decreases to V_t.
What will this chapter help you become familiar with regarding MOSFETs?
Its physical structure, operation, terminal characteristics, and dc circuit applications.
How many terminals does the enhancement-type MOSFET have?
Four terminals: gate (G), source (S), drain (D), and substrate/body (B).
What is the typical range for the width (W) of an n-channel enhancement-type MOSFET?
30 nm to 100 μm.
How does doubling the channel length affect the drain current (iD)?
It decreases the drain current.
What is the threshold voltage (Vt) in an NMOS transistor?
The gate voltage at which a sufficient number of mobile electrons accumulate to form a conducting channel.
What effect does a negative vDS have in a p-channel MOSFET?
It causes a current iD to flow from source to drain.
What is the term used when the channel depth at the drain end reduces to zero?
Channel pinch-off.
What are the two major types of three-terminal semiconductor devices?
MOSFET and bipolar junction transistor (BJT).
What three factors determine the conductance (gDS) of the channel?
The product of (μn Cox), (W/L), and vOV (or vGS - Vt).
What is mixed-signal design?
The implementation of both analog and digital functions on the same IC chip.
What is the significance of CMOS technology in relation to bipolar devices?
By 2019, CMOS technology had taken over many applications previously possible only with bipolar devices.
What is the typical thickness range of the oxide layer (tox) in the n-channel enhancement-type MOSFET?
1 nm to 10 nm.
What happens to the drain current (iD) when the overdrive voltage is doubled?
The drain current increases.
In what type of substrate is an n-channel MOSFET formed?
In a p-type substrate.
What happens to the MOSFET when the voltage between drain and source (v_DS) is kept small?
The device operates as a linear resistance controlled by v_GS.
What enhances the channel in an enhancement-type MOSFET?
Increasing v_GS above the threshold voltage V_t.
What does the channel behave as for small vDS?
A linear resistance controlled by the overdrive voltage vOV.
What is the significance of integrated circuits (ICs) in relation to MOSFETs?
MOSFETs allow for packing large numbers on a single chip, enabling sophisticated VLSI digital circuits.
What dimensions does the process transconductance parameter have?
Amperes per volt squared (A/V²).
What forms the gate electrode of the enhancement-type MOSFET?
Metal deposited on top of the silicon dioxide layer.
What does the saturation portion of the iD-vDS curve look like?
It is a horizontal straight line.
What is the significance of the overdrive voltage (vOV) in MOSFET operation?
It is used to determine the saturation-mode drain current (iD).
Why is the current in the gate terminal of a MOSFET extremely small?
Because the gate electrode is electrically insulated from the device body by the oxide layer.
What is the resistance of the path between drain and source when zero gate voltage is applied?
Very high resistance, of the order of 10^12 Ω.
Why are three-terminal semiconductor devices more useful than two-terminal ones?
They can be used in applications like signal amplification and digital logic, controlling current with voltage.
How can the relationship between i_D and v_DS be derived?
By replacing v_OV in the equation with the appropriate value.
Why did NMOS technology supplant PMOS technology?
Because electron mobility is higher than hole mobility, resulting in greater gains and speeds for NMOS transistors.
What is the significance of the overdrive voltage (v_OV) in MOSFET operation?
It determines the channel depth at the source end.
What is the MOSFET transconductance parameter (k_n)?
It is the product of the process transconductance parameter and the transistor aspect ratio (W/L), with dimensions of A/V².
What are the typical dimensions for length (L) and width (W) in the n-channel enhancement-type MOSFET?
L = 20 nm to 1 μm and W = 30 nm to 100 μm.
What is the minimum value of vDS needed to operate a transistor in saturation?
It is determined by the specific operating conditions and parameters of the MOSFET.
What happens to the pn junctions formed by the substrate in normal MOSFET operation?
They are kept reverse biased at all times.
What is one of the applications discussed in this chapter regarding MOSFETs?
Analyzing and designing circuits that contain MOS transistors, resistors, and dc sources.
