Developing the next-generation sensor with high sensitivity at low priceFeatured Technologies
Successful manufacturing of an infrared sensor using carbon nanotubes
April 10, 2023
Carbon nanotube is a substance that NEC discovered for the first time in the world. This time, NEC developed an infrared sensor that draws on the characteristics of this substance and succeeded in arraying the elements and checking its operation. We interviewed the researchers about this sensor that may replace conventional infrared sensors as the next-generation sensor.
Dual approaches: ultra-high sensitivity and low-cost commercial production
― What is an infrared sensor using carbon nanotubes?
Yuge: It is an infrared sensor with very high sensitivity. Conventional infrared sensors use a substance called vanadium oxide. Our sensor uses carbon nanotubes, which have a temperature coefficient of resistance (TCR)―a measure for sensitivity―more than three times that of vanadium oxide. This means that it is capable of sensing the target in darker, farther places. It can also detect temperature differences in detail and help create precise images. Additionally, the improvement in the basic performance enables further weight and cost reduction of devices like thermographic cameras for temperature check, which do not require high resolutions. We are estimating that we can achieve a weight reduction of one-third to one-fifth of the weight of conventional models, to say the least.
Sano: Present high-definition infrared sensors have been used in a wide range of applications, including quality inspections in space business and manufacturing, structural degradation diagnoses, surveillance, and aviation and automotives. Our new sensor has a game-changing impact on the fundamentals of such infrared sensors. The current infrared sensors using vanadium oxide has been used in the world for the past 15 to 20 years. In recent years, however, an emergence of a new infrared sensor with drastically enhanced performance was anticipated. Our new sensor answers such expectation.
In particular, infrared sensors are considered to be an essential part of autonomous driving of automobiles and drones. An infrared camera can capture people and cars by sensing heat, even at night or when visible light cameras cannot function due to strong light or reflection from snow. Together with LiDAR, we expect this to be one of the critical players in sensing. Once we complete the carbon nanotube sensor, safety can be further improved by being able to detect objects in darker, farther places.
Yuge: As of present, we have succeeded in creating an array of 640 x 480 pixels and confirmed its operation. We are now moving on to the development and prototyping for imaging. We are taking a dual approach for this sensor: micromachine-integrated MEMS* aimed at ultra-high sensitivity and achieving lower price with the same level of performance as before.
- *Micro Electro Mechanical Systems (MEMS): Micromachine that integrates an electronic circuit and a mechanical system
Leveraging the know-how of discovering carbon nanotubes
― What made it possible for NEC to develop this sensor?
Yuge: Carbon nanotube was discovered by Dr. Iijima, NEC’s Senior Research Fellow, in 1991. Since then, NEC has actively continued research and development for the applied use of carbon nanotubes.
NEC’s previous developments, specifically, using carbon nanotubes as ink to be applied to devices and as a film, are also adopted in this development of a low-cost sensor. The extraction technology of carbon nanotubes with semiconductor properties that NEC developed jointly with AIST in 2018 is a core technology that set a starting point for the new sensor. This proprietary technology enabled the extraction of semiconductor properties with high purity from carbon nanotubes, which consist of both metal and semiconductor types. We learned that applying the carbon nanotubes extracted using this technology to the infrared sensor achieves excellent effect, which marked the outset of this sensor development.
The deep knowledge and the accumulation of proprietary technologies related to our carbon nanotubes led to the development of the new sensor.
Sano: In addition to that, NEC has been manufacturing infrared sensors. The manufacturing has now been transferred to NEC Platforms, Ltd., a group company, but we are still producing high-performance infrared sensors, including MEMS sensors, at our plant in Japan. Thanks to this know-how and environment, NEC is able to very efficiently and smoothly implement sensor development.
Tanaka: You may think that it’s simply about switching the material of the sensor from vanadium oxide to carbon nanotubes, but it’s not that easy. A change in the material also changes the optimal structure, and when the structure changes, so does the way to utilize the characteristics of the material. For this reason, we need to work on research and prototyping in parallel. In that sense, it is NEC’s advantage that we have both laboratories and plants. This makes it possible for us to seamlessly implement the trial-and-error cycle of research and development within the group for improvement. In fact, I was visiting the plant from yesterday to just now to receive the prototypes. Not very many organizations in the world may be capable of providing such an environment.
Carbon nanotubes have performance potentials yet to be explored
― Tell us about your future prospects.
Yuge: First, we will be working on imaging over the next whole year. Then we will do demonstrations in-house and externally with the aim for early commercialization.
On the other hand, I feel that we have not yet exerted the full potential of carbon nanotubes. We have not yet reached the calculated figures, and moreover, there may even be potential abilities that we have not realized yet. One of our challenges for future research and development will be to fully use the characteristics of carbon nanotubes.
― For what applications will this sensor be used in society in the near future?
Sano: As mentioned previously, it will definitely be used for autonomous driving of automobiles and drones. With its high resolution, this sensor will also be useful for assisting nighttime piloting of helicopters and other aircrafts. To give an example, helicopters for rescue missions in mountainous areas is understood to be difficult, particularly nighttime flying, due to the risk of contact with electric wires. This sensor may be able to support such flying operations.
Yuge: For human applications, since this enables more detailed sensing of body temperature, there may be a use in medical settings. Various other applications are possible, including monitoring of patients’ health conditions.
Tanaka: If less expensive sensors can be mass-produced, they can be installed in a variety of spots in society while working in cooperation with other sensors. Then we may start seeing their use in something like digital twins. It may also be useful in applications of a larger scale, such as city surveillance or infrastructure monitoring.
Comment from Dr. Iijima
Infrared sensors using carbon nanotubes (CNTs) expands the application of CNTs to areas that bolster safety and security in our lives, in which I am placing high expectations.
Both the technology that extracts semiconductor-type CNTs, which is suitable for creating high-performance devices with large area and thin profile at low cost, and the printed-circuit manufacturing process technology that uses CNTs in ink are technologies developed with Mr. Yuge’s team.
I hope that R&D of CNTs will flourish toward its contribution to society.
The infrared sensor using carbon nanotubes drastically outperforms conventional infrared sensors. The use of carbon nanotubes, a material discovered by NEC, in the detector (bolometer) offers higher resolution than conventional sensors using vanadium oxide. We have confirmed that the temperature coefficient of resistance (TCR)―a measure for sensitivity―of carbon nanotube is more than three times that of vanadium oxide.
The application of carbon nanotubes to the bolometer owes largely to the proprietary technology that extracts carbon nanotubes with semiconductor properties with high purity, which was developed jointly with AIST and Meijo Nano Carbon Co., Ltd. in 2018. This technology not only enables the application of carbon nanotubes to sensors, but also led to the success of creating element arrays. The prototyping of sensors draws on NEC’s long-standing experience in manufacturing infrared sensors. While the manufacturing has now been transferred to NEC Platforms, Ltd., a group company, the close collaboration between its laboratory and the production plant in Otsuki, Yamanashi Prefecture, is accelerating development.
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