Ferroelectric Tunnel FET Sub-60mV Switching
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Solution Overview
Problem
Conventional FETs face limitations in power dissipation due to subthreshold swing, which restricts voltage scaling and switching range, and existing tunnel FETs and ferroelectric FETs rely on single principles for abrupt transitions, leading to high voltage and power consumption.
Innovation Solution
A ferroelectric Tunnel FET combining band-to-band tunneling and negative capacitance principles in a single device architecture, utilizing a ferroelectric gate stack for steep transitions and low off-current, enabling lower voltage and power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional FET is used, then device simplicity is maintained, but subthreshold swing is limited to 60 mV/decade and power dissipation increases
Solution Approach 1:
The patent combines two distinct switching mechanisms (band-to-band tunneling in TFET and negative capacitance from ferroelectric FET) into a single hybrid device structure. The ferroelectric gate stack is integrated with the tunnel FET channel, creating a unified device that achieves sub-60 mV/decade subthreshold swing through the synergistic interaction of quantum tunneling and ferroelectric field amplification, thereby reducing power dissipation without requiring separate devices
Solution Approach 2:
The device employs a composite gate stack structure consisting of ferroelectric material (e.g., Pb(Zr,Ti)O3 or Pb1-xLaxZr1-yTiyO3) combined with dielectric layers and metal electrodes. This composite material architecture enables the simultaneous realization of negative capacitance effect and field coupling to the tunneling junction, achieving both abrupt switching and low power consumption in a single integrated structure
2Reliability
If single-principle switching devices (TFET or FeFET) are used, then device structure is simpler, but switching abruptness and off-current are insufficient
Solution Approach 1:
The patent merges the abrupt switching characteristic of TFET (based on band-to-band tunneling) with the field amplification capability of ferroelectric FET (based on negative capacitance). The ferroelectric layer in the gate stack provides voltage amplification that enhances the electric field at the tunneling junction, thereby improving switching abruptness and reducing off-current without requiring complex multi-device structures
Solution Approach 2:
The ferroelectric gate stack introduces a positive feedback mechanism where the polarization state of the ferroelectric material amplifies the gate voltage effect on the channel. This feedback loop enhances the switching abruptness by creating a regenerative effect that rapidly transitions the device between off and on states, overcoming the limitations of single-principle devices
3Use of energy by moving object
If voltage scaling is pursued in conventional FET, then power dissipation decreases, but subthreshold swing limitation prevents further scaling
Solution Approach 1:
The patent fundamentally changes the voltage-current relationship parameter by utilizing quantum mechanical band-to-band tunneling instead of thermionic emission. This parameter change enables subthreshold swing below the thermal limit of 60 mV/decade, allowing voltage scaling to continue while maintaining low power dissipation. The ferroelectric gate stack further amplifies this effect by providing negative capacitance that enhances the voltage control over the tunneling current
4Area of stationary object
If 1T-1C FeRAM structure is used, then memory functionality is achieved, but capacitor scaling limits further miniaturization
Solution Approach 1:
The patent extracts and removes the separate capacitor component from the traditional 1T-1C FeRAM structure. By integrating the ferroelectric functionality directly into the gate stack of the tunnel FET, the device combines memory retention (through ferroelectric polarization) and switching functionality (through band-to-band tunneling) in a single transistor structure, eliminating the need for a discrete capacitor and enabling further miniaturization
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ferroelectric Tunnel FET achieves significantly reduced subthreshold swing and ultra-low off-current, making it suitable for low-power memory applications and enabling abrupt switching with lower voltage operation compared to existing devices.
Implementation Method 1
combining two switching mechanisms (band-to-band tunneling and negative capacitance) in a single device
Implementation Method 2
exploits two physics principles in a single device architecture to obtain a very steep transition from off to on state: (i) positive feedback in the gate stack and (ii) band-to-band tunneling in a gated p-i-n junction
Implementation Method 3
The resulting device could present a hysteretic abrupt characteristic due to the ferroelectric gate stack
Data Source
AI summary
A Ferroelectric tunnel FET switch as ultra-steep (abrupt) switch with subthreshold swing better than the MOSFET limit of 60 mV/decade at room temperature combining two key principles: ferroelectric gate stack and band-to-band tunneling in gated p-i-n junction, wherein the ferroelectric material included in the gate stack creates, due to dipole polarization with increasing gate voltage, a positive feedback in the capacitive coupling that controls the band-to-band (BTB) tunneling at the source junction of a silicon p-i-n reversed bias structure, wherein the combined effect of BTB tunneling and ferroelectric negative capacitance offers more abrupt off-on and on-off transitions in the present proposed Ferroelectric tunnel FET than for any reported tunnel FET or any reported ferroelectric FET.