Ultraconformable Integrated Wireless Charging Micro-Supercapacitor Skin.

Conformable and wireless charging energy storage devices play important roles in enabling the fast development of wearable, non-contact soft electronics. However, current wireless charging power sources are still restricted by limited flexural angles and fragile connection of components, resulting in the failure expression of performance and constraining their further applications in health monitoring wearables and moveable artificial limbs. Herein, we present an ultracompatible skin-like integrated wireless charging micro-supercapacitor, which building blocks (including electrolyte, electrode and substrate) are all evaporated by liquid precursor. Owing to the infiltration and permeation of the liquid, each part of the integrated device attached firmly with each other, forming a compact and all-in-one configuration. In addition, benefitting from the controllable volume of electrode solution precursor, the electrode thickness is easily regulated varying from 11.7 to 112.5 µm. This prepared thin IWC-MSC skin can fit well with curving human body, and could be wireless charged to store electricity into high capacitive micro-supercapacitors (11.39 F cm-3) of the integrated device. We believe this work will shed light on the construction of skin-attachable electronics and irregular sensing microrobots.

A broadband 3D microtubular photodetector based on a single wall carbon nanotube-graphene heterojunction.

In this paper, a three-dimensional (3D) photodetector based on a single wall carbon nanotube (SWCNT) and graphene heterojunction has been fabricated by a self-rolled-up process. In the designed structure, graphene acted as the conductive channel and SWCNTs absorbed the incident light ranging from the visible to near-infrared bands. Compared to planar (two-dimensional, 2D) devices, 3D microcavities provided a natural resonant cavity to enhance the optical field, which improved the photoresponsivity. This 3D heterojunction photodetector realized a broadband photodetection from 470 to 940 nm with an ultrahigh photoresponsivity of 4.9 × 104 A W-1 (@ 590 nm) and 1.9 × 104 A W-1 (@ 940 nm), a fast photoresponse speed of 1.6 ms, and an excellent sensitivity of 2.28 × 1011 Jones. Besides, the fabricated photodetector showed favorable mid-infrared detection with a photoresponsivity of 3.08 A W-1 at 10.6 µm. Moreover, the photodetector exhibited a promising room-temperature imaging capability. The 3D heterojunction photodetector would provide a feasible pathway to realize graphene-based photodetectors with high performance and could be extended to be integrated with other light absorptive materials.

High-performance one-dimensional MOSFET array photodetectors in the 0.8-µm standard CMOS process.

This paper reports a series of novel photodetectors based on one-dimensional array of metal-oxide-semiconductor field-effect transistors (MOSFETs), which were fabricated using the standard 0.8-µm complementary metal oxide semiconductor (CMOS) process. Normally, the metal fingers of MOSFET must be manufactured above active region in standard CMOS process, causing MOSFET insensitive to light. The proposed photodetectors use the metal fingers of MOSFETs in a one-dimensional array to form periodical slit structures, which make the transmittance of incident light higher, due to the surface plasmons (SPs) resonance effect. The number of parallel MOSFETs in one-dimensional array is 3, 5, 7, 9 and 11. The experimental results show that all responsivities (Rv) are greater than 103 A/W within visible and near-infrared spectra under room temperature and a maximum value of 1.40 × 105 A/W is achieved, which is at least one order of magnitude larger than those of published photodetectors. Furthermore, a minimum noise equivalent power (NEP) of 5.86 fW/Hz0.5 at 30 Hz and a maximum detectivity (D*) of 2.21 × 1013 Jones are obtained. The photodetectors still have good signal-to-noise ratio when the bandwidth is 1 GHz. At the same time, the optical scanning imaging was completed by utilizing the photodetectors. This combination of high Rv, excellent NEP, high speed and broad spectrum range photodetectors will be widely used in imaging systems.

A Novel Terahertz Detector Based on Asymmetrical FET Array in 55-nm Standard CMOS Process.

This paper reports a novel, one-dimensional dense array of asymmetrical metal-oxide-semiconductor field-effect-transistor (MOSFET) THz detector, which has been fabricated in GlobalFoundries 55-nm CMOS technology. Compared with other technologies, the Si-based complementary metal-oxide-semiconductor (CMOS) dominates in industrial applications, owing to its easier integration and lower cost. However, as the frequency increases, the return loss between the antenna and detector will increase. The proposed THz detector has a short-period grating structure formed by MOSFET fingers in the array, which can serve as an effective antenna to couple incident THz radiation into the FET channels. It not only solved the problem of return loss effectively, but also greatly reduced the detector area. Meanwhile, since the THz signal is rectified at both the source and drain electrodes to generate two current signals with equal amplitude but opposite directions, the source drain voltage is not provided to reduce the power consumption. This leads to a poor performance of the THz detector. Therefore, by using an asymmetric structure for the gate fingers position to replace the source drain voltage, the performance of the detector in the case of zero power consumption can be effectively improved. Compared with the symmetrical MOSFET THz detector, Rv is increased by 183.3% and NEP is decreased by 67.7%.

Highly Sensitive Photodetectors Based on Monolayer MoS2 Field-Effect Transistors.

Molybdenum disulfide (MoS2) is a promising candidate for the development of high-performance photodetectors, due to its excellent electric and optoelectronic properties. However, most of the reported MoS2 phototransistors have adopted a back-gate field-effect transistor (FET) structure, requiring applied gate bias voltages as high as 70 V, which made it impossible to modulate each detecting device in the fabricated array. In this paper, buried-gate FETs based on CVD-grown monolayer MoS2 were fabricated and their electric and photoelectric properties were also systematically investigated. A photoresponsivity of around 6.86 A/W was obtained at 395 nm, under the conditions of zero gate bias voltage and a light power intensity of 2.57 mW/cm2. By application of a buried-gate voltage of 8 V, the photoresponsivity increased by nearly 10 times. Furthermore, the response speed of the buried-gate MoS2 FET phototransistors is measured to be around 350 ms. These results pave the way for MoS2 photodetectors in practical applications.

High-responsivity photodetector using a grating-gate MOSFET in the 0.8-µm standard CMOS process.

This letter reports a novel photodetector based on a metal-oxide-semiconductor field-effect transistor with a grating-gate structure, which was fabricated by employing the standard 0.8-µm complementary metal-oxide-semiconductor process. The use of a periodical slit structure allows the channel to be generated and exposed on the shallow surface, which makes the transmission and absorption of incident light more efficient, due to the surface plasmon resonance effect. The experimental results show that a responsivity (Rv) greater than 100 A/W was achieved within visible and near-infrared spectra under room temperature. Furthermore, a minimum noise equivalent power of 8.2 fW/Hz0.5 at 15 Hz and a maximum detectivity (D*) of 1.7 × 1012 Jones were obtained. It is believed that the photodetector will be widely used in communication or imaging systems.

A novel temperature sensor based on three-dimensional buried-gate graphene field effect transistor.

Temperature sensor is one of the primarily developed and most proverbially utilized sensors. Owing to the limitations of their characteristics (stability, thermal conductivity, and thermal contact area), traditional temperature sensors may exhibit drawbacks of high production cost and large volume. In this paper, a three-dimensional (3D) buried-gate graphene field effect transistors (GFETs) are proposed as a novel sensor for temperature detection, which possess a 3D microtube structure by self-rolled-up technology. Compared to conventional two-dimensional (2D) devices, the 3D devices would have tinier area and higher integration. Two main reasons that would affect the resistance of the graphene are the graphene electro-phonon coupling and the thermal expansion effect. In addition, by applying the COMSOL Multiphysics software, it has been demonstrated that the microtube would deform to a certain extent when the temperature increases. And the strain on the 3D devices is proved to be greater than that of the 2D devices. Experimental results show that 3D GFETs could realize temperature detection between 30 °C and 150 °C, and its resistance increases with temperature rising. Furthermore, the maximum achieved temperature coefficient of resistance (TCR) is 0.41% °C-1and the hysteresis error is only 3.85%. By virtue of the 3D microtube, not only more superior temperature detection could be achieved, but also more devices are integrated in unit area. The 3D temperature sensor possesses superior sensitivity, repeatability and stability, which contributes a new approach to develop the high-performance temperature sensor.

Monolayer MoS2photodetectors with a buried-gate field-effect transistor structure.

Unlike zero-bandgap graphene, molybdenum disulfide (MoS2) has an adjustable bandgap and high light absorption rate, hence photodetectors based on MoS2have attracted tremendous research attention. Most of the reported MoS2photodetectors adopted back-gate field-effect transistor (FET) structure due to its easy fabrication and modulation features. However, the back-gate FET structure requires very high gate voltage up to 100 V, and it is impossible to modulate each device in an array with this structure independently. This work demonstrated a monolayer MoS2photodetector based on a buried-gate FET structure whose experimental results showed that both the electrical and photoelectrical properties could be well modulated by a gate voltage as low as 3 V. A photoresponsivity above 1 A W-1was obtained under a 395 nm light-emitting diode light illumination, which is over 2 orders of magnitude higher than that of a reported back-gate photodetector based on monolayer MoS2(7.5 mA W-1). The photoresponsivity can be further improved by increasing the buried gate voltage and source-drain voltage. These results are of significance for the practical applications of MoS2photodetectors, especially in the low voltage and energy-saving areas.

A novel three-dimensional Ag nanoparticles/reduced graphene oxide microtubular field effect transistor sensor for NO2 detections.

A novel three-dimensional (3D) microtubular NO2 field effect transistor (FET) sensor has been fabricated from 2D reduced graphene oxide (rGO) nanosheets decorated with Ag nanoparticles, by applying the self-roll-up technique. The electrical properties of 2D and 3D Ag NP/rGO FET sensors have been investigated and compared. Finally, the performance of the 3D sensors has been demonstrated, where the preliminary results show that our 3D Ag NP/rGO FET NO2 sensor exhibits a relatively fast response (response time of 116 s) to 20 parts per million NO2 with a response of 4.92% at room temperature at zero bias voltage and 2 V source-drain bias voltage. Moreover, characteristics of our 3D Ag NP/rGO FET sensors, e.g. response, response and recovery times, have been demonstrated to be tuned by adjusting the applied source-drain and gate biases. Compared to the 2D geometry, our 3D geometry occupies less device area, but with the same sensing area. This study provides a new way to optimize sensing device performance, and promotes its development for miniaturized and integrated gas-sensing applications for indoor health and safety detection, outdoor environmental monitoring, industrial pollution monitoring and beyond.

A Novel Three-Dimensional Ag nanoparticles/rGO Microtubular Field Effect Transistor Sensor for NO2Detections.

Abstract：A novel three-dimensional (3D) microtubular NO2FET sensor has been fabricated from the two-dimensional (2D) reduced graphene oxide (rGO) nanosheets decorated with Ag nanoparticles, by applying the self-roll up technique. The electrical properties of 2D and 3D FET Ag NPs/rGO sensors have been investigated and compared. Finally, the performance of the 3D sensors has been demonstrated, where the preliminary results shown that our 3D FET Ag NPs/rGO NO2sensor exhibit a relative fast response (response time of 116 s) to 20 part per million (ppm) NO2with a response of 4.92 % at room temperature at zero bias voltage and 2 V source-drain bias voltage. Moreover, the characteristics of our 3D FET Ag NPs/rGO sensors, e.g. response, response and recovery times have been demonstrated to be tuned by adjusting the applied source-drain and gate biases. Compared to 2D geometry, our 3D geometry occupied less device area, but with the same sensing area. This study would provide a new way to optimize sensing devices performance, and promote its developments for miniaturized and integrated gas sensing applications for indoor health and safety detections, outdoor environmental monitoring, industrial pollution monitoring and beyond.

High sensitivity ultraviolet detection based on three-dimensional graphene field effect transistors decorated with TiO2 NPs.

A three-dimensional (3D) ultraviolet (UV) photodetector was fabricated by decorating a tubular graphene field-effect transistor (GFET) with titanium dioxide (TiO2) nanoparticles (NPs). The unique tubular architecture not only provides a natural 3D optical resonant microcavity to enhance the optical field inside it, but also increases the light-matter interaction area. Strong UV absorption in the TiO2 NPs creates a number of electron-hole pairs, where the electrons are transferred to graphene, while the holes are trapped within the TiO2 NPs, leading to a strong photogating effect on the graphene channel conductance. The photoresponsivity of our 3D GFET photodetector decorated with TiO2 NPs was demonstrated up to 475.5 A W-1 at 325 nm, which is about 2 orders of magnitude higher than that of a 3D GFET photodetector without the TiO2 NP decoration (1 A W-1), and over 3 orders of magnitude higher than that of a recently reported UV photodetector based on the graphene/vertical Ga2O3 nanowire array heterojunction (0.185 A W-1). Moreover, the photoresponsivity and photoresponse speed of the device can be easily tuned by applying a small gate bias (≤3 V) and/or changing the source-drain bias. These results indicate that the photoresponsivities of graphene-based photodetectors can be significantly improved by exploiting 3D graphene structures and integrating graphene with semiconducting light harvesters simultaneously.