Silicon electronic devices are the most important category of devices in the microelectronics science and technology, and have played an important role in the development of science and technology in the last century. Carbon-based electronic devices have shown a great technical potential since the beginning of this century. Especially, carbon nanotubes integrate a variety of physical and chemical properties due to good electrical, optical and mechanical properties thereof. Currently, for medical and wearable devices such as medical sensors, electronic skin etc., the carbon nanotubes have been used as candidates for research on full flexible Carbon Nanotube Thin Film Transistors (CNT-TFTs).
Piezoelectric sensors are a category of sensors developed based on piezoelectric effect dielectric. The so-called piezoelectric effect refers to that when some dielectric is deformed as an external force is applied in a certain direction, a polarization phenomenon may occur in the dielectric, and at the same time opposite charges, i.e., positive and negative charges, appear in two opposite surfaces of the dielectric. After the external force is removed, the dielectric will return to an uncharged state. This phenomenon is called a direct piezoelectric effect. When the direction of the applied force changes, the polarity of the charges will change accordingly. On the contrary, when an electric field is applied in a polarization direction of the dielectric, the dielectric may be deformed, and after the electric field is removed, the deformation of the dielectric disappears. This phenomenon is called an inverse piezoelectric effect.
For conventional piezoelectric sensors, all the thin films associated with sensor components are manufactured on a silicon chip. When a piezoelectric thin film layer is manufactured using the silicon chip, an oven annealing process is implemented at a high temperature of 600° C.-700° C., and remaining related integrated circuits are manufactured using conventional semiconductor processes. However, such processes can only result in rigid piezoelectric sensor components, and these piezoelectric sensors are limited to unidirectional pressure sensing.
In conclusion, the conventional piezoelectric sensors can only realize unidirectional pressure sensing, but cannot realize omni-directional pressure sensing.