Graphene Field-Effect Transistor Temperature Sensor

Temperature detection is of great significance in many fields,such as environmental monitoring,industrial and agricultural production,and biomedicine,etc.Accurate measurement can ensure the normal operation of each work.As the core component of the temperature detection system,the temperature sensor has been widely studied.Traditional thermal resistive and thermocouple temperature sensors have problems such as large size,large self-heating effect,and low sensitivity,which can’t meet the growing demand for miniaturization and integration.Therefore,it is urgent to develop a high-sensitivity,small-sized high-performance MEMS temperature sensor.The development of MEMS temperature sensors relies on the evolution of temperature-sensitive materials and novel structures.Based on this,this paper proposes a three-dimensional（3D）structured graphene field effect transistor（GFET）,where the single-layer graphene with silicon nitride（Si N_x）self-rolled-up microtubules are combined to achieve temperature detection.The main works of this paper are as follows:1.The temperature sensitivity mechanisms of graphene temperature sensors were studied,mainly due to the joint action of two effects.One effect is that the mobility and concentration of graphene carriers vary with temperature under the influence of electrophonon interactions,intrinsic excitation,and coulomb potential action of electrical impurities,resulting in the change in the conductivity of graphene.Another effect is that the thermal expansion of the device structure will cause thermal stress on graphene,causing graphene to deform and open its band gap.Eventually,the electrical conductivity of graphene varys with temperature.2.Realized the preparation of 3D GFET-type temperature sensors in high volume and integration.The buried gate electrode was used to effectively reduce the gate voltage.The Si N_x pressure/tension double stress layer drived two-dimensional（2D）GFET self-rolled-up,separating graphene from the substrate,reducing the effects of noise and slow substrate heat dissipation.The morphological characteristics and composition of the device were analyzed by scanning electron microscopy（SEM）and Raman spectroscopy.The electrical performance of the device was analyzed by semiconductor parametric instrument.3.The temperature sensitivity characteristics of the 3D GFET type temperature sensor between 30 and 150℃ were analyzed.The resistance of 3D GFET increased linearly with temperature.The 3D GFET has good repeatability,whose linearity is better than that of 2D GFET.The resistance temperature coefficient（TCR）of the 3D GFET temperature sensor at 150℃ is 0.41%℃^-1,which is higher than conventional metal temperature sensor.However,after long-term preservation in the air,the temperature sensitivity of the 3D GFET without a protective layer structure deteriorated,and the linearity decreased significantly.4.A planar graphene temperature sensor with a nano-film protective layer was prepared.The protective effect of different thicknesses and materials on graphene were explored.The results show that graphene temperature sensors with 400 nm Si N_x（PECVD）can reach an operating temperature of 600℃.The addition of a protective layer can effectively improve the temperature measurement range of the device.In summary,this paper proposed a 3D buried-gate graphene field effect transistor（GFET）as a new MEMS temperature sensor,with high sensitivity,repeatability and stability.The protective performance of the protective layer is also studied,which can improve the temperature measurement range of the planar graphene temperature sensitive sensor.This paper provides a new research direction for achieving high-performance,miniaturized temperature sensors.