Qian-Yi Xie

A Graphene-Based Resistive Pressure Sensor with Record-High Sensitivity in a Wide Pressure Range

Pressure sensors are a key component in electronic skin (e-skin) sensing systems. Most reported resistive pressure sensors have a high sensitivity at low pressures (<5 kPa) to enable ultra-sensitive detection. However, the sensitivity drops significantly at high pressures (>5 kPa), which is inadequate for practical applications. For example, actions like a gentle touch and object manipulation have pressures below 10 kPa, and 10–100 kPa, respectively. Maintaining a high sensitivity in a wide pressure range is in great demand. Here, a flexible, wide range and ultra-sensitive resistive pressure sensor with a foam-like structure based on laser-scribed graphene (LSG) is demonstrated. Benefitting from the large spacing between graphene layers and the unique v-shaped microstructure of the LSG, the sensitivity of the pressure sensor is as high as 0.96 kPa−1 in a wide pressure range (0 ~ 50 kPa). Considering both sensitivity and pressure sensing range, the pressure sensor developed in this work is the best among all reported pressure sensors to date. A model of the LSG pressure sensor is also established, which agrees well with the experimental results. This work indicates that laser scribed flexible graphene pressure sensors could be widely used for artificial e-skin, medical-sensing, bio-sensing and many other areas.

Graphene Dynamic Synapse with Modulatable Plasticity

The synaptic activities in the nervous system is the basis of memory and learning behaviors, and the concept of biological synapse has also spurred the development of neuromorphic engineering. In recent years, the hardware implementation of the biological synapse has been achieved based on CMOS circuits, resistive switching memory, and field effect transistors with ionic dielectrics. However, the artificial synapse with regulatable plasticity has never been realized of the device level. Here, an artificial dynamic synapse based on twisted bilayer graphene is demonstrated with tunable plasticity. Due to the ambipolar conductance of graphene, both behaviors of the excitatory synapse and the inhibitory synapse could be realized in a single device. Moreover, the synaptic plasticity could also be modulated by tuning the carrier density of graphene. Because the artificial synapse here could be regulated and inverted via changing the bottom gate voltage, the whole process of synapse development could be imitated. Hence, this work would offer a broad new vista for the 2D material electronics and guide the innovation of neuro-electronics fundamentally.

In Situ Tuning of Switching Window in a Gate-Controlled Bilayer Graphene-Electrode Resistive Memory Device

A resistive random access memory (RRAM) device with a tunable switching window is demonstrated for the first time. The SET voltage can be continuously tuned from 0.27 to 4.5 V by electrical gating from -10 to +35 V. The gate-controlled bilayer graphene-electrode RRAM can function as 1D1R and potentially increase the RRAM density.

Fabrication techniques and applications of flexible graphene-based electronic devices

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

A record flexible piezoelectric KNN ultrafine-grained nanopowder-based nanogenerator

We explore a type piezoelectric material 0.9525(K0.5Na0.5NbO3)-0.0475LiTaO3 (KNN-LTS) which can be used to fabricate nanogenerator with high output voltage and current due to its high piezoelectric constant (d33). Because of its unique structure mixed with multi-wall carbon nanotube and polydimethylsiloxane, the output voltage is up to 53 V and the output current is up to 15 uA (current density of 12.5 uA/cm2) respectively. The value of the output voltage and output current represent the highest level in the piezoelectric field reported to date. The KNN-LTS nanopowder-based nanogenerator can also be used as a sensitive motion detection sensor.

A Flexible 360-Degree Thermal Sound Source Based on Laser Induced Graphene

A flexible sound source is essential in a whole flexible system. It’s hard to integrate a conventional sound source based on a piezoelectric part into a whole flexible system. Moreover, the sound pressure from the back side of a sound source is usually weaker than that from the front side. With the help of direct laser writing (DLW) technology, the fabrication of a flexible 360-degree thermal sound source becomes possible. A 650-nm low-power laser was used to reduce the graphene oxide (GO). The stripped laser induced graphene thermal sound source was then attached to the surface of a cylindrical bottle so that it could emit sound in a 360-degree direction. The sound pressure level and directivity of the sound source were tested, and the results were in good agreement with the theoretical results. Because of its 360-degree sound field, high flexibility, high efficiency, low cost, and good reliability, the 360-degree thermal acoustic sound source will be widely applied in consumer electronics, multi-media systems, and ultrasonic detection and imaging.

A novel thermal acoustic device based on porous graphene

A thermal acoustic (TA) device was fabricated by laser scribing technology. Polyimide (PI) can be converted into patterned porous graphene (PG) by laser’s irradiation in one step. The sound pressure level (SPL) of such TA device is related to laser power. The theoretical model of TA effect was established to analyze the relationship between the SPL and laser power. The theoretical results are in good agreement with experiment results. It was found that PG has a flat frequency response in the range of 5-20 kHz. This novel TA device has the advantages of one-step procedure, high flexibility, no mechanical vibration, low cost and so on. It can open wide applications in speakers, multimedia, medical, earphones, consumer electronics and many other aspects.

Super high frequency lithium niobate surface acoustic wave transducers up to 14 GHz

We report lithium niobate (LiNbO3) surface acoustic wave (SAW) transducers with the smallest linewidth and the highest resonant frequency. A record 30 nm wide, 200 nm period (λ0) nanofabricated metallic structure on non-conductive LiNbO3 enables a frequency exceeding 14 GHz. At higher frequencies, greater data throughputs and improved sensor sensitivity are enabled. A systematic study of SAW devices from λ0=200-800 nm is presented taking into account crystal orientation, device design, patterning strategies, and resonant modes. The device performance metrics such as frequency, g-factor, insertion loss, and coupling coefficient are measured in detail and these metrics are also found to exceed the results of other recent state-of-the-art devices, when compared.

Tunable and wearable high performance strain sensors based on laser patterned graphene flakes

Tunable and wearable strain sensors with high gauge factor (GF) and large strain range based on laser patterned graphene flakes (LPGF) are demonstrated in this paper. The performance can be adjusted by laser patterning, resulting in a preferable GF (up to 457) or strain range (over 100%), both of which are significantly higher than most of the state-of-the-art graphene strain sensors. Most importantly, the tunable strain sensors with high GF and large strain range can be fabricated simultaneously by a one-step laser patterning. These tunable strain sensors can meet the demands of monitoring both subtle and large human motions, indicating that they will have great potentials in health care, voice recognition, gesture control and many other areas.

Electrical thermal acoustic point source based on mems technology

This work demonstrated, for the first time, an electro-thermoacoustic (ETA) point source based on Point-Contact-Structure (PCS) realized by MEMS technology based on suspended aluminum nanowires. The novel type of device improves the performance at low frequency down to 500 Hz, enhances the efficiency of ETA device by over 7 folds and widen the 3 dB range of low frequency range comparing to conventional suspended aluminum nanowires (AW) ETA devices. The highest sound pressure level (SPL) achieved by PCS acoustic device is 67 dB at 1 cm with 74 mW AC input. The novel device works in a less than ± 3 dB fluctuation mode which is realized by the enhancement of SPL at low frequency.