"No bypass circuit" nanowire bridge growth scheme
Micro gas detector
Information technology such as artificial intelligence, wearable equipment, and the Internet of Things is developing rapidly. It requires a large number of sensors to provide support. Big data and cloud computing services also require various sensors to collect data in real time to support it. However, the current sensors have problems such as low localization, low-end products, weak technological innovation, and backward production processes.
Recently, a team of professors from the School of Electronic Science and Technology of Dalian University of Technology invented the “nanowire bridging growth technology” for leak-free current, which solved the problem of array assembly, electrode contact and material stability of nanowire devices, and developed high reliability and low power. A highly sensitive GaN nanowire gas sensor that can be extended to biometric detection and stress and strain detection.
Micro-nano sensing has a "can"
In recent years, semiconductor integrated circuit chips (ICs) have developed rapidly, driving the rise of the Internet of Things and artificial intelligence industries. "If the IC is likened to the human brain (processing information), the sensor is equivalent to the human sensory organ (getting information), and the IC and the sensor are interdependent."
However, the speed of development of sensors, especially micro-nano sensors, lags far behind the development of ICs. Micro-nano sensors and sensor chips will be another major industry after the IC industry.
The smallest sensor currently widely used is a MEMS sensor.
MEMS sensors (MEMS) are new sensors manufactured using microelectronics and micromachining technology. Its internal structure is generally on the order of micrometers or even nanometers and is an independent intelligent system. Compared with traditional sensors, it has the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for mass production, easy integration and intelligentization. At the same time, the feature size on the order of micrometers makes it possible to perform functions not possible with some conventional mechanical sensors.
"Compared with MEMS devices, semiconductor nanowires are 1000 times smaller and 1 million times smaller. Therefore, nanowires are the smallest device and ideal for micro-nano sensors."
Compared with traditional bulk materials and thin film materials, semiconductor nanowires have many unique advantages: large specific surface area can improve the sensitivity of the device, easy to deform can improve the integration of materials, nano-scale light guide and conductive channels can make single nanometer Line photonic devices. In addition, the excellent mechanical properties of the nanowires and the flexible structure make it more flexible and can form a core cladding and a cross-grid structure.
In addition, nanowires are difficult to manipulate and it is difficult to position them. "And the contact area between the nanowire and the metal electrode is very small, so the electrode contact resistance is very large, nearly two orders of magnitude higher than the resistance of the nanowire itself."
Nanowire sensor "long" came out
In order to solve a series of problems such as difficult positioning of nanowires and small contact area of electrodes, in 2004, Hewlett-Packard and the University of California invented a "nanowire bridging growth technology." By etching the recesses on the SOI substrate, the nanowires grow from one side of the recess and abut the other side, so that metal electrodes can be prepared on the side surfaces of the recesses.
This "growth" approach to the integration of nanowires and sidewalls avoids the fabrication of metal electrodes on the surface of the nanowires, which reduces electrode contact resistance by two orders of magnitude and noise by three orders of magnitude. In addition, there is no need to arrange and position the nanowires, which simplifies the preparation process and eliminates surface contamination and damage of the nanowires.
However, HP's nanowire bridging growth program has not been promoted. Because of the method, in the growth process of the nanowire, a polycrystalline film (parasitic deposition layer) is usually deposited on the bottom of the groove, and the parasitic deposition layer generates a large bypass current, which greatly deteriorates the performance of the nanowire device.
To this end, the expert team first studied the parasitic deposition effect in nanowire bridging growth, and invented a bridging growth method that combines the airflow occlusion effect and the surface passivation effect to solve the parasitic deposition problem. The researchers used a new grooved scheme and groove structure to avoid material deposition at the bottom of the groove and achieve bridged growth of the nanowires.
"Using GaN buffer layer, by adjusting the growth conditions of nanowires, such as gas flow, catalyst, temperature gradient, etc., the position, direction, diameter and length of nanowire growth can be changed, and nanowires can be realized from GaN nanowires, nanoneedle to microcolumn. Controllable growth."
It is reported that GaN materials are third-generation semiconductors with excellent stability and biocompatibility, high temperature resistance, oxidation resistance, acid and alkali corrosion resistance, and are suitable for the detection of liquid and gas samples in severe environments. “Experiments have shown that corrosion in hydrofluoric acid for 48 hours does not affect GaN nanowire resistance, and its application is very extensive.”
On this basis, the team developed an integrated nanowire gas sensor, the GaN nanowire gas sensor. After testing, the sensor can work at room temperature, the resistance change rate of <8% in 8 months, and the detection limit of NO2 is 0.5ppb, featuring high stability, low power consumption and high sensitivity.
This technology is the first to realize "no leakage current" GaN bridged nanowires, and the development of GaN nanowire gas sensors will drive the development of sensor chips.
Sensor chip is coming soon
Micro-nano sensors are subversive technologies with enormous innovation and market space. In recent years, micro-nano sensors have become one of the hotspots of government and social capital investment. “The micro-sodium sensor is closely related to the development of the Internet of Things and 5G. It is widely used in mobile phones, automobiles, medical and consumer fields, and its development situation is very good.”
The head of the Department of Electronics and Computer Engineering at the University of Michigan said that the previous sensors required three components: electronics, wireless networking systems, and wireless networking systems. In the future, sensor and sensor applications will be ubiquitous. When they are combined into a network, they can achieve better sensor networks in a small environment through micro-nano sensors.
“It is possible to load millions of sensors in just 1 millimeter. Such devices can provide very small chips and monitor data in a timely, timely and accurate manner, which will help us to play in different energy systems and power systems. effect."
The team will focus on the development of lower power, smaller GaN nanowire gas sensors and try to make sensor chips. “The ideal situation is to work with integrated circuit chips to combine sensing, control, and processing signals for a wider range of applications.”