NEMS Devices with Ferroelectric Negative Capacitor for Sub-1V Actuation
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Solution Overview
Problem
The integration of nanoelectromechanical systems (NEMS) in next-generation chips is hindered by fabrication challenges, particularly the scaling of airgaps to achieve low power dissipation and ideal switching characteristics, as existing technologies face issues with sub-1V actuation, tunneling currents, and surface forces leading to non-ideal switching and high standby power dissipation.
Innovation Solution
The introduction of a ferroelectric negative capacitor connected in series with a NEMS device, stabilizing the system in a negative capacitance regime, allowing for voltage amplification and reducing the effective airgap without physical scaling, thereby achieving sub-1V pull-in voltage and hysteresis-free operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the airgap is scaled down to a few nanometers to achieve sub-1V actuation and low power dissipation, then the pull-in voltage is reduced and power savings are achieved, but fabrication becomes extremely challenging and non-ideal physical effects such as tunneling current and surface forces degrade device performance
Solution Approach 1:
A ferroelectric negative capacitor is introduced as an intermediary component between the voltage source and the NEMS device. This negative capacitor amplifies the applied voltage, effectively reducing the pull-in voltage requirement without physically scaling the airgap. The negative capacitance regime provides voltage multiplication, allowing sub-1V operation while maintaining a larger, fabricable airgap distance
Solution Approach 2:
The invention changes the electrical parameter regime by operating the ferroelectric capacitor in its negative capacitance region. This parameter change enables voltage amplification where the voltage across the NEMS device can be negative even when positive voltage is applied to the combined structure, effectively achieving sub-1V actuation without physical dimension changes
2Loss of energy
If the airgap is scaled down to achieve low power dissipation, then standby power is reduced, but tunneling current is introduced which degrades subthreshold swing and increases power dissipation
Solution Approach 1:
The ferroelectric negative capacitor serves as a mediator that decouples the relationship between airgap size and power dissipation. By providing voltage amplification through negative capacitance, the system can operate with low pull-in voltage without requiring a small airgap, thereby avoiding tunneling current while still achieving low power dissipation through reduced actuation voltage
3Ease of operation
If the airgap is reduced to achieve sub-1V pull-in voltage, then switching characteristics improve, but surface forces such as Van der Waals and Casimir forces cause stiction
Solution Approach 1:
The negative capacitor acts as an intermediary that provides the necessary voltage amplification to overcome surface forces without requiring the movable electrode to be positioned extremely close to the fixed electrode. This maintains sufficient separation distance to minimize Van der Waals and Casimir forces while still achieving effective switching
4Power
If a ferroelectric capacitor is operated in the negative capacitance regime, then voltage amplification is achieved, but the system becomes unstable without a series capacitor
Solution Approach 1:
The invention merges the ferroelectric negative capacitor with a series capacitor (the NEMS device capacitance) to create a stable combined structure. The series connection allows the system to operate in the negative capacitance regime and achieve voltage amplification while the total applied voltage remains constant, providing the necessary stability for practical operation
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
This approach significantly reduces the pull-in voltage and travel range of NEMS devices, enabling dramatic power savings and improved switching characteristics, making them suitable for memory and display applications while avoiding fabrication challenges.
Implementation Method 1
Ferroelectric (FE) negative capacitors are known. Recently, Salahuddin and Datta has reported a ferroelectric negative capacitor connected in series with a classical gate oxide transistor in which the gate voltage was amplified
Implementation Method 2
An FE capacitor is characterized by a negative capacitance around zero charge
Implementation Method 3
A Micro/Nano electromechanical system (M/NEMS) consists of a pair of electrodes one fixed and the other movable separated by an airgap
Implementation Method 4
The stability comes from the fact that the charge state of the combined structure is determined by, not the FE alone, but the energetics of the overall structure
Data Source
AI summary
An electrical circuit comprising at least two negative capacitance insulators connected in series, one of the two negative capacitance insulators is biased to generate a negative capacitance. One of the negative capacitance insulators may include an air-gap which is part of a nanoelectromechnical system (NEMS) device and the second negative capacitance insulator includes a ferroelectric material. Both of the negative capacitance insulators may be located between the channel and gate of a field effect transistor. The NEMS device may include a movable electrode, a dielectric and a fixed electrode and arranged so that the movable electrode is attached to at least two points and spaced apart from the dielectric and fixed electrode, and the ferroelectric capacitor is electrically connected to either of the electrodes.