Define channel hot electron (CHE) injection in MOSFETs and its effects.
1 Answer
Channel Hot Electron (CHE) injection is a phenomenon that occurs in Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) when high-energy electrons gain sufficient energy from the electric field in the channel region, leading to their injection into the gate oxide and subsequently into the gate electrode. This injection of hot electrons can cause various effects that can affect the performance and reliability of the MOSFET.
Here's a more detailed explanation of CHE injection and its effects:
Hot Electron Generation: In a MOSFET, when a voltage is applied between the drain and source terminals (Vds), an electric field is established in the channel region under the gate oxide. This electric field accelerates some of the electrons in the channel to high energies, creating "hot" or high-energy electrons.
Injection into Gate Oxide: Some of these high-energy electrons can gain enough energy to overcome the energy barrier at the interface between the silicon channel and the gate oxide. As a result, they are injected into the gate oxide layer.
Impact Ionization: The injected hot electrons can undergo impact ionization in the gate oxide, creating electron-hole pairs. The holes generated in this process can cause a positive charge buildup in the oxide, which can modify the threshold voltage of the MOSFET and potentially affect its behavior.
Trapping: Some of the injected hot electrons may get trapped in the gate oxide, leading to a permanent positive charge buildup. This trapped charge can alter the gate oxide's properties, reduce its breakdown voltage, and degrade the MOSFET's performance over time. This phenomenon is known as positive oxide trapped charge or positive bias temperature instability (PBTI).
Reverse Bias Stress: In certain cases, when a reverse voltage is applied to the drain terminal, known as "negative bias stress," the trapped hot electrons can be released back into the channel region. This process is called "reverse hot carrier injection" and can result in threshold voltage shifts and other performance degradation.
Reliability Issues: CHE injection and its associated effects can degrade MOSFET performance over time, leading to shifts in threshold voltage, increased leakage current, and reduced device lifetime. The reliability of MOSFETs under accelerated stress conditions can be a concern in high-performance and high-reliability applications.
To mitigate CHE injection effects, device designers employ various techniques, such as using high-quality gate oxides, optimizing device dimensions, and implementing specialized process steps. Additionally, circuit-level measures like biasing and design for safe operating conditions can also be used to minimize the impact of CHE injection in MOSFETs.
Here's a more detailed explanation of CHE injection and its effects:
Hot Electron Generation: In a MOSFET, when a voltage is applied between the drain and source terminals (Vds), an electric field is established in the channel region under the gate oxide. This electric field accelerates some of the electrons in the channel to high energies, creating "hot" or high-energy electrons.
Injection into Gate Oxide: Some of these high-energy electrons can gain enough energy to overcome the energy barrier at the interface between the silicon channel and the gate oxide. As a result, they are injected into the gate oxide layer.
Impact Ionization: The injected hot electrons can undergo impact ionization in the gate oxide, creating electron-hole pairs. The holes generated in this process can cause a positive charge buildup in the oxide, which can modify the threshold voltage of the MOSFET and potentially affect its behavior.
Trapping: Some of the injected hot electrons may get trapped in the gate oxide, leading to a permanent positive charge buildup. This trapped charge can alter the gate oxide's properties, reduce its breakdown voltage, and degrade the MOSFET's performance over time. This phenomenon is known as positive oxide trapped charge or positive bias temperature instability (PBTI).
Reverse Bias Stress: In certain cases, when a reverse voltage is applied to the drain terminal, known as "negative bias stress," the trapped hot electrons can be released back into the channel region. This process is called "reverse hot carrier injection" and can result in threshold voltage shifts and other performance degradation.
Reliability Issues: CHE injection and its associated effects can degrade MOSFET performance over time, leading to shifts in threshold voltage, increased leakage current, and reduced device lifetime. The reliability of MOSFETs under accelerated stress conditions can be a concern in high-performance and high-reliability applications.
To mitigate CHE injection effects, device designers employ various techniques, such as using high-quality gate oxides, optimizing device dimensions, and implementing specialized process steps. Additionally, circuit-level measures like biasing and design for safe operating conditions can also be used to minimize the impact of CHE injection in MOSFETs.