Robust Tunability and Newly Emerged Q Resonance of Ba0.8Sr0.2TiO3-Based Microwave Capacitors under Gamma Irradiations.

The complex resonance of dielectric quality factor Q, combined with a capacitance tunability n higher than 3:1 without any dispersion, was achieved in the voltage-tunable interdigital capacitors (IDCs) based on epitaxial Ba0.8Sr0.2TiO3 ferroelectric thin films across the microwave L (1-2 GHz), S (2-4 GHz), and C (4-8 GHz) bands at room temperature. The resonant Q and n features were driven by the microwave responses of the ferroelectric nanodomains engineered in the films. To promote their application in space radiation environments, the evolutions of Q and n both as functions of frequency f (1-8 GHz) and applied electric field E (0-240 kV/cm) were systematically investigated under a series of gamma-ray irradiations up to 100 kGy. The robust capacitance tunability was accompanied by the emergence of an additional Q resonance at 2.3 GHz in most post-irradiated devices, which is ascribed to extra polar nanoregions of expanded surface lattices associated with oxygen vacancies induced by irradiations.

Flexible and Transparent Artificial Synapse Devices Based on Thin-Film Transistors with Nanometer Thickness.

BACKGROUND: Artificial synaptic behaviors are necessary to investigate and implement since they are considered to be a new computing mechanism for the analysis of complex brain information. However, flexible and transparent artificial synapse devices based on thin-film transistors (TFTs) still need further research. PURPOSE: To study the application of flexible and transparent thin-film transistors with nanometer thickness on artificial synapses. MATERIALS AND METHODS: Here, we report the design and fabrication of flexible and transparent artificial synapse devices based on TFTs with polyethylene terephthalate (PET) as the flexible substrate, indium tin oxide (ITO) as the gate and a polyvinyl alcohol (PVA) grid insulating layer as the gate insulation layer at room temperature. RESULTS: The charge and discharge of the carriers in the flexible and transparent thin-film transistors with nanometer thickness can be used for artificial synaptic behavior. CONCLUSION: In summary, flexible and transparent thin-film transistors with nanometer thickness can be used as pressure and temperature sensors. Besides, inherent charge transfer characteristics of indium gallium zinc oxide semiconductors have been employed to study the biological synapse-like behaviors, including synaptic plasticity, excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), and long-term memory (LTM). More precisely, the spike rate plasticity (SRDP), one representative synaptic plasticity, has been demonstrated. Such TFTs are interesting for building future neuromorphic systems and provide a possibility to act as fundamental blocks for neuromorphic system applications.

Transparent Nano Thin-Film Transistors for Medical Sensors, OLED and Display Applications.

BACKGROUND: Transparent thin-film transistors (TFTs) have received a great deal of attention for medical sensors, OLED and medical display applications. Moreover, ultrathin nanomaterial layers are favored due to their more compact design architectures. METHODS: Here, transparent TFTs are proposed and were investigated under different stress conditions such as temperature and biases. RESULTS: Key electrical characteristics of the sensors, such as threshold voltage changes, illustrate their linear dependence on temperature with a suitable recovery, suggesting the potential of the devices to serve as medical temperature sensors. The temperature conditions changed in the range of 28°C to 40°C, which is within the standard human temperature testing range. The thickness of the indium-gallium-zinc oxide semiconductor layer was as thin as only 5-6 nm, deposited by mature radio-frequency sputtering which also showed good repeatability. Optimal bending durability caused by mechanical deformation was demonstrated via suitable electrical properties after up to 600 bending cycles, and by testing the flexible device at a different bending radii ranging from 48 mm to 18 mm. CONCLUSION: In summary, this study suggests that the present transparent nano TFTs are promising candidates for medical sensors, OLED and displays which require transparency and stability.

Implementation of PPI with Nano Amorphous Oxide Semiconductor Devices for Medical Applications.

BACKGROUND: Electronic devices which mimic the functionality of biological synapses are a large step to replicate the human brain for neuromorphic computing and for numerous medical research investigations. One of the representative synaptic behaviors is paired-pulse facilitation (PPF). It has been widely investigated because it is regarded to be related to biological memory. However, plasticity behavior is only part of the human brain memory behavior. METHODS: Here, we present a phenomenon which is opposite to PPF, i.e., paired-pulse inhibition (PPI), in nano oxide devices for the first time. The research here suggests that rather than being enhanced, the phenomena of memory loss would also be possessed by such electronic devices. The device physics mechanism behind memory loss behavior was investigated. This mechanism is sustained by historical memory and degradation manufactured by device trauma to regulate characteristically stimulated origins of artificial transmission behaviors. RESULTS: Under the trauma of a memory device, both the signal amplitude and signal time stimulated by a pulse are lower than the first signal stimulated by a previous pulse in the PPF, representing a new scenario in the struggle for memory. In this way, more typical human brain behaviors could be simulated, including the effect of age on latency and error generation, cerebellar infarct, trauma and memory loss pharmacological actions (such as those caused by hyoscines and nitrazepam). CONCLUSION: Thus, this study developed a new approach for implementing the manner in which the brain works in semiconductor devices for improving medical research.

Temperature Dependence Of AOS Thin Film Nano Transistors For Medical Applications.

BACKGROUND: A novel temperature dependent amorphous nano oxide semiconductor (AOS) thin-film transistor (TFT) is reported here for the first time, which is vastly different from conventional behavior. In the literature, the threshold voltage of TFTs decreases with increasing temperature. Here, the threshold voltage increased at higher temperatures, which is different from previously reported results and was repeated on different samples. METHODS: Electrical experiments (such as I-V measurements and photoelectron spectrometer experiments) were performed in order to explain such behavior. Double sweeping gate voltage measurements were performed to investigate the mechanism for the temperature dependent behavior. RESULTS: It was found that there was a change of trap charge under thermal stress, which was released after the stress. CONCLUSION: Non-Arrhenius behaviors (including a linear behavior) were obtained for the amorphous nano oxide thin-film transistors within 303~425 K, suggesting their potential to be adjusted by measurement processes and be applied as temperature sensors for numerous medical applications.

A newly developed transparent and flexible one-transistor memory device using advanced nanomaterials for medical and artificial intelligence applications.

Background: Artificial intelligence (AI) integrated circuits (IC) have memory devices as the key component. Due to more complex algorithms and architectures required by neuroscience and other medical applications, various memory structures have been widely proposed and investigated by involving nanomaterials, such as memristors. Methods: Due to reliability issues of mass production, the dominant memory devices in many computers are still dynamic random access memory (DRAM). A DRAM has one transistor and one capacitor, and so it contains two devices and requires a more compact design to replace. Results: A one-transistor memory device which is more compact than DRAM is proposed. As far as the authors know, this is the first/novel flexible and transparent one-transistor memory device without any additional process to make a typical transistor and which is based on polyvinyl alcohol. By using indium-titanium-oxide (ITO) as the metal gate, PVA as the dielectric layer and In-Ga-Zn-O (IGZO) as the channel, the memory is implemented mainly based on amorphous oxides and transparent flexible nanomaterials. The charge storage for the memory function was investigated here and is attributed to the mechanism of charge trapping between the ITO/IGZO junctions. It shows typical artificial synaptic transmission behaviors such as EPSC (excitatory postsynaptic currents). Conclusion: Such a first flexible and transparent one-transistor memory device based on PVA has one capacitor less than DRAM and could be a potential and promising candidate as an alternative for DRAM, especially in the highly complex AI chips needed for numerous medical applications. The flexible memory nanodevice based on flexible dielectrics such as PVA, which shows typical memory and artificial synaptic behaviors, could also be suitable for portable, flexible, transparent or skin-like medical applications.