87 research outputs found
Memory Window in Ferroelectric Field-Effect Transistors: Analytical Approach
A memory window of ferroelectric field-effect transistors (FeFETs), defined
as a separation of the HIGH-state and the LOW-state threshold voltages, is an
important measure of the FeFET memory characteristics. In this study, we
theoretically investigate the relation between the FeFET memory window and the
P-E hysteresis loop of the ferroelectric gate insulator, and derive a compact
model explicitly described by material parameters. It is found that the memory
window is linearly proportional to the ferroelectric polarization for the small
polarization regime, and converges to the limit value of 2 x coercive field x
thickness when the remanent polarization is much larger than permittivity x
coercive field. We discuss additional factors that possibly influence the
memory window in actual devices such as the existence of interlayer (no direct
impact), interface charges (invalidity of linear superposition between the
ferroelectric and charge-trapping hysteresis), and minor-loop operation
(behavior equivalent to the generation of interface charges)
Metabolic Fingerprinting in Toxicological Assessment Using FT-ICR MS
Detection of the toxicity of a candidate compound at an early stage of drug
development is an emerging area of interest. It is difficult to determine all of
the effects of metabolism of a compound using traditional approaches such as
histopathology and serum biochemistry. The goal of a metabolomics approach is to
determine all metabolites in a living system, with the potential to detect and
identify biomarkers involved in toxicity onset. Here, we summarize the metabolic
fingerprints for detection and identification of metabolic changes and
biomarkers related to drug-induced toxicity using Fourier transform ion
cyclotron resonance mass spectrometry (FT-ICR MS)
Invited; HfZrO-based ferroelectric capacitors and FETs for ultralow-power signal processing
Since the discovery of ferroelectricity in HfO2-based dielectric films in 2011 [1], MFM capacitors and FETs using HfO2-based thin films as dielectrics have attracted strong interest. Thus, active research and developments have been conducted for various applications including memory, logic, and AI computing with extremely low power consumption. In this paper, we introduce our recent research on a variety of HfZrO2 (HZO)-based ferroelectric devices such as FeRAM [2-3], FeFET memory [4-8], anti-ferroelectric FETs [9-10] and reservoir computing devices [11-13], for ultralow-power signal processing.The high polarization reversal voltage associated with the high coercive field of HZO films makes it difficult to achieve the low voltage operation of HZO FeRAM. Here, scaling HZO film thickness is effective in a reduction of the supply voltage of FeRAM with HZO MFM capacitors. It has been found through a systematic study on ferroelectric characteristics of Hf0.5Zr0.5O2 films with a thickness from 9.5 to 2.8 nm [2, 3] that scaling HZO film thickness to 4-5 nm can reduce operating voltage below 1 V (~0.8 V) with sufficient 2Pr by performing 106 cycles of wakeup. Also, the electric field causing dielectric breakdown can significantly increase by HZO scaling. The experimental endurance characteristic of 4-nm-thick HZO has indicated that the maximum cycle times determined by dielectric breakdown is around 1010 and 1012 times at 4 MV/cm and 3 MV/cm (1.2 V), respectively, under a pulse voltage operation of 200 kHz.
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Non-volatile hybrid optical phase shifter driven by a ferroelectric transistor
Optical phase shifters are essential elements in photonic integrated circuits
(PICs) and function as a direct interface to program the PIC. Non-volatile
phase shifters, which can retain information without a power supply, are highly
desirable for low-power static operations. Here a non-volatile optical phase
shifter is demonstrated by driving a III-V/Si hybrid metal-oxide-semiconductor
(MOS) phase shifter with a ferroelectric field-effect transistor (FeFET)
operating in the source follower mode. Owing to the various polarization states
in the FeFET, multistate non-volatile phase shifts up to 1.25{\pi} are obtained
with CMOS-compatible operation voltages and low switching energy up to 3.3 nJ.
Furthermore, a crossbar array architecture is proposed to simplify the control
of non-volatile phase shifters in large-scale PICs and its feasibility is
verified by confirming the selective write-in operation of a targeted FeFET
with a negligible disturbance to the others. This work paves the way for
realizing large-scale non-volatile programmable PICs for emerging computing
applications such as deep learning and quantum computing
Ultrahigh-sensitivity optical power monitor for Si photonic circuits
A phototransistor is a promising candidate as an optical power monitor in Si
photonic circuits since the internal gain of photocurrent enables high
sensitivity. However, state-of-the-art waveguide-coupled phototransistors
suffer from a responsivity of lower than A/W, which is insufficient for
detecting very low power light. Here, we present a waveguide-coupled
phototransistor consisting of an InGaAs ultrathin channel on a Si waveguide
working as a gate electrode to increase the responsivity. The Si waveguide gate
underneath the InGaAs ultrathin channel enables the effective control of
transistor current without optical absorption by the gate metal. As a result,
our phototransistor achieved the highest responsivity of approximately
A/W among the waveguide-coupled phototransistors, allowing us to detect light
of 621 fW propagating in the Si waveguide. The high responsivity and the
reasonable response time of approximately 100 s make our phototransistor
promising as an effective optical power monitor in Si photonics circuits
Non-volatile optical phase shift in ferroelectric hafnium zirconium oxide
A non-volatile optical phase shifter is a critical component for enabling
large-scale, energy-efficient programmable photonic integrated circuits (PICs)
on a silicon (Si) photonics platform. While ferroelectric materials like BaTiO3
offer non-volatile optical phase shift capabilities, their compatibility with
complementary metal-oxide-semiconductor (CMOS) fabs is limited. Hence, the
search for a novel CMOS-compatible ferroelectric material for non-volatile
optical phase shifting in Si photonics is of utmost importance. Hafnium
zirconium oxide (HZO) is an emerging ferroelectric material discovered in 2011,
which exhibits CMOS compatibility due to the utilization of high-k dielectric
HfO2 in CMOS transistors. Although extensively studied for ferroelectric
transistors and memories, its application in photonics remains relatively
unexplored. Here, we show the optical phase shift induced by ferroelectric HZO
deposited on a SiN optical waveguide. We observed a negative change in
refractive index at a 1.55 um wavelength in the pristine device regardless of
the direction of an applied electric filed. We achieved approximately pi phase
shift in a 4.5-mm-long device with negligible optical loss. The non-volatile
multi-level optical phase shift was confirmed with a persistence of > 10000 s.
This phase shift can be attributed to the spontaneous polarization within the
HZO film along the external electric field. We anticipate that our results will
stimulate further research on optical nonlinear effects, such as the Pockels
effect, in ferroelectric HZO. This advancement will enable the development of
various devices, including high-speed optical modulators. Consequently,
HZO-based programmable PICs are poised to become indispensable in diverse
applications, ranging from optical fiber communication and artificial
intelligence to quantum computing and sensing
Modulation bandwidth improvement of III-V/Si hybrid MOS optical modulator by reducing parasitic capacitance
In this work, we numerically and experimentally examined the impact of parasitic capacitance on the modulation bandwidth of a III-V/Si hybrid metal-oxide-semiconductor (MOS) optical modulator. The numerical analysis revealed that the parasitic capacitance between the III-V membrane and the Si slab should be considered to achieve high-speed modulation, particularly in the case of a thick gate oxide. We also fabricated a high-speed InGaAsP/Si hybrid MOS optical modulator with a low capacitance using a SiO2-embedded Si waveguide. The fabricated device exhibited a modulation efficiency of 0.245 Vcm and a 3 dB bandwidth of up to 10 GHz. Clear eye patterns with 25 Gbps non-return-to-zero (NRZ) modulation and 40 Gbps 4-level pulse amplitude modulation (PAM-4) were obtained without pre-emphasis
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