A reconfigurable gated Schottky diode is proposed as new high-density and low-power synaptic device that has near-linear changes in conductance. The device has a reverse current of less than 12 nA/μm ...and an effective device area of 6F 2 . Since the Al/poly-Si Schottky junction is located on the bottom gate, which has a SiO 2 /Si 3 N 4 /SiO 2 charge trap layer, the effective Schottky barrier height is modulated by the bottom gate bias or by the amount of charge trapped in the Si 3 N 4 layer. The Schottky reverse current has an exponential relationship with the effective Schottky barrier height associated with the amount of stored charge, and the amount of stored charge is logarithmically proportional to the number of potentiation pulses. Because the exponential and logarithmic relationships cancel each other out, a near-linear conductance response to the number of potentiation pulses is obtained from the proposed device.
Fine control over the physicochemical structures of carbon electrocatalysts is important for improving the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable ...Zn–air batteries. Covalent organic frameworks (COFs) are considered good candidate carbon materials because their structures can be precisely controlled. However, it remains a challenge to impart bifunctional electrocatalytic activities for both the ORR and OER to COFs. Herein, a pyridine‐linked triazine covalent organic framework (PTCOF) with well‐defined active sites and pores is readily prepared under mild conditions, and its electronic structure is modulated by incorporating Co nanoparticles (CoNP‐PTCOF) to induce bifunctional electrocatalytic activities for the ORR and OER. The CoNP‐PTCOF exhibits lower overpotentials for both ORR and OER with outstanding stability. Computational simulations find that the p‐band center of CoNP‐PTCOF down‐shifted by charge transfer, compared to pristine PTCOF, facilitate the adsorption and desorption of oxygen intermediates on the pyridinic carbon active sites during the reactions. The Zn–air battery assembled with bifunctional CoNP‐PTCOF exhibits a small voltage gap of 0.83 V and superior durability for 720 cycles as compared with a battery containing commercial Pt/C and RuO2. This strategy for modulating COF electrocatalytic activities can be extended for designing diverse carbon electrocatalysts.
Pyridine‐linked triazine covalent organic framework (PTCOF) with well‐defined carbon active sites and pores is readily prepared, and its electronic structure is effectively modulated by incorporating Co nanoparticles into the framework (CoNP‐PTCOF) to improve the bifunctional electrocatalytic activity for the oxygen reduction reaction and oxygen evolution reaction in Zn–air batteries. A rechargeable Zn–air battery with bifunctional CoNP‐PTCOF exhibits outstanding performance with superior durability.
In this work, the low-frequency noise (LFN) characteristics of hafnium-zirconium oxide (HZO) ferroelectric field-effect transistors (FeFETs) with and without high-pressure forming gas annealing (HPA) ...treatment are investigated. The origin of <inline-formula> <tex-math notation="LaTeX">1/ {f} </tex-math></inline-formula> noise in the FeFET without HPA is changed from carrier number fluctuation to Hooge's mobility fluctuation after wake-up due to the remote phonon scattering from the polarized HZO. Also, Hooge's parameter is increased by the program/erase (P/E) cycling-induced stress. On the contrary, only the correlated mobility fluctuation is increased after the wake-up in the FeFET with HPA. Furthermore, the LFN of the FeFET with HPA shows robustness to P/E cycling-induced stress after the wake-up, showing superb endurance performance.
In this paper, we propose an adaptive quantization method that can easily transfer the weights, which are trained in software network with floating point operation, to the real synaptic devices in ...hardware-based neural networks and maintain high performance. An n-type gated Schottky diode is investigated as a synaptic device, and the conductance behavior of this device is modeled successfully. Max value normalization and <inline-formula> <tex-math notation="LaTeX">3\sigma </tex-math></inline-formula> normalization are applied to the weights trained with an accuracy of 98.29% on fully connected neural network (<inline-formula> <tex-math notation="LaTeX">784\times 256\times10 </tex-math></inline-formula>) using software network. Then, the weights are quantized using the adaptive quantization method and can be transferred by adjusting the number of identical pulses applied to the synaptic devices. After applying the adaptive quantization method, accuracy rates of 98.09% and 97.20% in MNIST classification are obtained for both max value normalization and <inline-formula> <tex-math notation="LaTeX">3\sigma </tex-math></inline-formula> normalization, respectively. The proposed quantization method works well even when there is nonideality of synaptic devices such as nonlinearity of conductance behavior, limited conductance levels, and variation of conductance.
In the field of gas sensor studies, most researchers are focusing on improving the response of the sensors to detect a low concentration of gas. However, factors that make a large response, such as ...abundant or strong adsorption sites, also work as a source of noise, resulting in a trade-off between response and noise. Thus, the response alone cannot fully evaluate the performance of sensors, and the signal-to-noise-ratio (SNR) should additionally be considered to design gas sensors with optimal performance. In this regard, thin-film-type sensing materials are good candidates thanks to their moderate response and noise level. In this paper, we investigate the effects of radio frequency (RF) sputtering power for deposition of sensing materials on the SNR of resistor- and field-effect transistor (FET)-type gas sensors fabricated on the same Si wafer. In the case of resistor-type gas sensors, the deposition conditions that improve the response also worsen the noise either by increasing the scattering at the bulk or damaging the interface of the sensing material. Among resistor-type gas sensors with sensing materials deposited with different RF powers, a sensor with low noise shows the largest SNR despite its small response. However, the noise of FET-type gas sensors is not affected by changes in RF power and thus there is no trade-off between response and noise. The results reveal different noise sources depending on the deposition conditions of the sensing material, and provide design guidelines for resistor- and FET-type gas sensors considering noise for optimal performance.
Response alone cannot fully evaluate the performance of sensors, and the signal-to-noise-ratio should additionally be considered to design gas sensors with optimal performance.
In this letter, we consider secure communications in multi-hop relaying systems, where full-duplex relays (FDRs) operate to enhance wireless physical layer security. Each FDR is designed to transmit ...jamming signals to the eavesdropper when it receives information signals from the previous adjacent node. The achievable secrecy rate with the proposed decode-and-forward (DF) FDRs are analyzed with a total transmit power constraint. The transmit power allocation problem is solved by using the geometric programming (GP) method. Numerical results present that the proposed FDRs significantly enhance the secrecy rate compared to the conventional half-duplex relays (HDRs).
Organic solid electrolytes offer an effective route for safe and high‐energy‐density all‐solid‐state Li metal batteries. However, it remains a challenge to devise a new strategy to promote the ...dissociation of strong ion pairs and the transport of ionic components in organic solid electrolytes. Herein, a zwitterionic covalent organic framework (Zwitt‐COF) with well‐defined chemical and pore structures is prepared as a solid electrolyte capable of accelerating the dissociation and transport of Li ions. The Zwitt‐COF solid electrolyte exhibits a high room‐temperature ionic conductivity of 1.65 × 10−4 S cm−1 with a wide electrochemical stability window. Besides, the Zwitt‐COF solid electrolyte displays stable Li plating/stripping behavior via effective inhibition of the formation of Li dendrites and dead Li, leading to superior long‐term cycle performance with retention of 99% discharge capacity and 98% Coulombic efficiency in an all‐solid‐state Li‐metal battery. Theoretical simulations reveal that the incorporation of zwitterionic groups into COF can facilitate the dissociation of strong ion pairs and reconstruct the AA‐stacking configuration by dissociative adsorption of Li+ ions on Zwitt‐COF producing linear hexagonal ion channels in the Zwitt‐COF solid electrolyte. This strategy based on Zwitt‐COF can provide an alternative way to construct various solid‐state Li batteries.
A zwitterionic covalent organic framework (Zwitt‐COF) is developed as a solid electrolyte for all‐solid‐state Li‐metal batteries. The Zwitt‐COF solid electrolyte exhibits a high room‐temperature ionic conductivity with a wide electrochemical window, leading to superior long‐term cycle performance in the battery. Theoretical simulations reveal that Zwitt‐COF promotes the dissociation of Li‐ion pairs and provides ion channels for effective Li+ transport.
Background and Aims The efficacy of palliative biliary drainage by using bilateral or unilateral self-expandable metal stents (SEMSs) for a malignant hilar biliary stricture (MHS) remains ...controversial. This prospective, randomized, multicenter study investigated whether bilateral drainage by using SEMSs is superior to unilateral drainage in patients with inoperable MHSs. Methods Patients with inoperable high-grade MHSs who underwent palliative endoscopic insertion of bilateral or unilateral SEMSs were enrolled. The main outcome measurements were the rate of primary reintervention for malfunction after successful placement of SEMSs, stent patency, technical and clinical success rates, adverse events, and survival duration. Results A total of 133 pathology-diagnosed patients were randomized to the bilateral group (n = 67) or the unilateral group (n = 66). The primary technical success rates were 95.5% (64/67) and 100% (66/66) in the bilateral and unilateral groups, respectively ( P = .244). The clinical success rates were 95.3% (61/64) and 84.9% (56/66), respectively ( P = .047). The primary reintervention rates based on the per-protocol analysis were 42.6% (26/61) in the bilateral group and 60.3% (38/63) in the unilateral group ( P = .049). The median cumulative stent patency duration was 252 days in the bilateral group and 139 days in the unilateral group. The risk of stent patency failure was significantly higher in the unilateral group (log-rank test; P < .01). In a multivariate Cox proportional hazard model to assess stent patency, bilateral SEMS placement was a favorable factor (adjusted hazard ratio 0.30, 95% confidence interval, 0.172-0.521; P < .001). Survival probability and late adverse events were not different between the 2 groups. Conclusions Unilateral and bilateral drainage strategies by using SEMSs had similar technical success rates, but bilateral drainage resulted in fewer reinterventions and more durable stent patency in patients with inoperable high-grade MHSs. (Clinical trial registration number: NCT02166970.)
We investigate the effects of length (<inline-formula> <tex-math notation="LaTeX">{L} </tex-math></inline-formula>) and width (<inline-formula> <tex-math notation="LaTeX">{W} ...</tex-math></inline-formula>) scaling on the low-frequency noise characteristics of the ferroelectric tunnel junction (FTJ). The FTJ is composed of metal/ferroelectric/dielectric/semicondu- ctor (TiN/HfZrO 2 /SiO 2 /<inline-formula> <tex-math notation="LaTeX">{n}^{+} </tex-math></inline-formula> Si). In the high-resistance state, 1/<inline-formula> <tex-math notation="LaTeX">{f} </tex-math></inline-formula> noise increases proportionally to 1/<inline-formula> <tex-math notation="LaTeX">{W}^{\alpha }{L}^{\beta } </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">\alpha \cong ~1 </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">\beta >1 </tex-math></inline-formula>), whereas the shot noise has no scaling dependence. In the low-resistance state, the 1/<inline-formula> <tex-math notation="LaTeX">{f} </tex-math></inline-formula> noise of the FTJ shows a more sensitive dependence on <inline-formula> <tex-math notation="LaTeX">{L} </tex-math></inline-formula> scaling than <inline-formula> <tex-math notation="LaTeX">{W} </tex-math></inline-formula> scaling since the switching and conduction mechanisms are more affected by the process-induced damaged edge regions.
The demand for gas sensing systems that enable fast and precise gas recognition is growing rapidly. However, substantial challenges arise from the complex fabrication process of sensor arrays, ...time‐consuming data transmission to an external processor, and high energy consumption in multi‐stage data processing. In this study, a gas sensing system using on‐chip annealing for fast and power‐efficient gas detection is proposed. By utilizing a micro‐heater embedded in the gas sensor, the sensing material of adjacent sensors in the same substrate can be easily varied without further fabrication steps. The response to oxidizing gas is constrained in metal oxide (MOX) sensing material with small grain sizes, as the depletion width of grain cannot extend beyond the grain size during the gas reaction. On the other hand, the response to reducing gases and humidity, which decrease the depletion width, is less affected by grain sizes. A readout circuit integrating a differential amplifier and dual FET‐type gas sensors effectively emphasizes the response to oxidizing gases by canceling the response to reducing gases and humidity. The selective on‐chip annealing method is applicable to various MOX sensing materials, demonstrating its potential for application in commercial fields due to its simplicity and expandability.
By utilizing embedded micro‐heaters for post‐deposition annealing, metal oxide grain size and gas responses of adjacent sensors in the same substrate can be controlled without further fabrication steps. The proposed dual FET‐type gas sensors with on‐chip annealing can directly determine the gas concentration in a mixed gas environment, introducing a new approach for a real‐time energy‐efficient gas sensing system.
