Graphene-based wearable temperature sensor and infrared photodetector on a flexible polyimide substrate

Abstract

This paper describes an approach to the fabrication of flexible electronics i.e., a wearable temperature sensor and infrared (IR) photodetector on flexible polyimide (PI) substrate. Solar exfoliated reduced graphene oxide (SrGO) and graphene flakes are used as the sensing materials for developing the sensors on a PI substrate. PI, apart from being flexible and compatible with microfabrication processes, also helps in reducing the mobility and recombination of the photo-generated electrons of graphene due of its dielectric nature, thus enabling IR detection. Current responsivity and external quantum efficiency of IR photodetector for graphene flakeand SrGO-based devices were found to be 0.4 A W −1 , 16.53% and 0.8 A W −1 , 33.06% respectively which are higher than those of commercially available photodetectors. In addition, we demonstrate an ultrasensitive wearable human body temperature sensor in the temperature range of 35 °C to 45 °C, wherein both graphene flakeand SrGO-based devices exhibited a negative temperature coefficient of −41.30 × 10 −4 °C−1 and −74.29 × 10 −4 °C−1 respectively, which are higher than commercially available counterparts. Plausible underlying mechanisms to both IR sensing and temperature sensing have been studied. Furthermore, as a proof of concept, we investigated the effect of IR radiation emitted by a human hand on the device. Interestingly it was found that the device was very sensitive to it, indicating that the sensor can be used for motion detection which has potential applications in security, surveillance etc. The strategy presented here provides a new, simple, cost effective approach for the fabrication of nextgeneration wearable and bio-implantable devices based on a polyimide substrate that can be easily integrated onto the surface of a leaf, skin, paper, clothes etc owing to its versatile nature.

Materials and Designs for Wearable Photodetectors

“…Polymers, such as polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polydimethylsiloxane (PDMS), have been widely utilized as substrates for wearable PDs for the inherent flexibility.…”

Highly Sensitive Temperature Sensor: Ligand‐Treated Ag Nanocrystal Thin Films on PDMS with Thermal Expansion Strategy

“…In order to realize highly sensitive and reliable temperature sensors with diverse forms, various types of sensors have been developed in conjunction with investigations related to emerging materials and fabrication processes. Four types of sensors with different sensing mechanisms have been widely studied: resistive temperature sensors, capacitive temperature sensors, transistor based, and PN‐junction based temperature sensors. Among these, resistive‐type temperature sensors are one of the most promising candidates owing to the following reasons: i) their simple geometry is compatible with various materials, substrates, and fabrication processes, such as solution processed materials, flexible substrates, and environmentally friendly fabrication processes, respectively, and ii) their simple and straightforward mechanism allows facile and direct measurement of temperature with high sensitivity.…”

Wearable Electronics Based on 2D Materials for Human Physiological Information Detection

“…2D materials represented by graphene can achieve high‐sensitivity, high‐precision, and fast‐response temperature detection via their atomic devices due to their excellent electromechanical properties, which exhibit the good conformal ability to body curve surface. To date, the investigation of body temperature sensors based on 2D materials mainly addressed on the graphene‐based devices …”

“…Using the calibration result between the value of resistance and temperature in the range of 35–36 °C, the calculated body temperature is 35.6 °C (Figure h). Interestingly, the solar exfoliated rGO exhibits infrared sensing properties due to the reduction of mobility and recombination of the photogenerated electrons in the graphene/PI composite . When the human hand close to the device, it shows the current decrease while the increase for hand far away from the device, indicating potential human body IR detection.…”