Terahertz is a frequency band of electromagnetic waves between millimeter waves and infrared, and the specific frequency is defined as 100GHz to 10THz. Compared with the millimeter wave band, terahertz has more abundant spectral resources, which is conducive to more accurate ranging, thickness measurement, motion perception, perspective imaging, and chemical composition identification. From a functional point of view, terahertz products include time-domain spectral analysis systems, radar systems, imaging systems, measurement instruments and communication systems. In these five fields, silicon-based integrated circuit technology has huge application potential.

　　1. Classification of Terahertz Products

Terahertz Time Domain Pulse and Spectral Analysis System

The operating frequency of high-end THz time-domain spectroscopy equipment generally covers from hundreds of GHz to several THz, far beyond the capability of solid-state circuits. At present, only terahertz time-domain short pulse sources based on photoelectric technology combined with bolometers or pyroelectric sensors can cover such a wide frequency range of excitation and detection. Foreign companies such as Advanced Photonix, Luna, Fraunhofer ITWM, etc. have launched high-precision thickness measurement systems for the thickness measurement of multi-layer structures inside industrial products, such as aircraft fuselage coating thickness, semiconductor material stack thickness, etc. Other large companies such as Advantest, Menlo Systems, TeraView, etc. have launched spectrometers, which are mainly used in scientific research, chemical industry, customs and other places. They can be used to identify material composition, identify drugs and drugs, and analyze semiconductor material defects. These devices are expensive, but the market has a strong demand for portable and low-cost small devices. Silicon-based integrated circuits are fully capable of low-frequency spectral analysis and millimeter-level thickness measurement with frequencies ranging from tens of GHz to hundreds of GHz.

Terahertz Radar System

The advantage of implementing radar systems at the terahertz frequency is that higher bandwidth can be obtained, resulting in more accurate range resolution. At present, commercial CMOS millimeter-wave radar chips are mainly 24, 60 and 77 GHz, with bandwidths of 1, 4 and 77 GHz, respectively. 5GHz, the theoretical distance resolution is from a few centimeters to a dozen centimeters, which is suitable for scenarios such as vehicles, smart transportation, smart buildings, and smart homes. However, in many industrial testing fields, this accuracy level cannot meet the requirements, and this market gap has been Filled by foreign companies, such as the SiGe technology 120GHz radar chip launched by Silicon Radar GmbH of Germany, which has been widely used in various domestic liquid level gauge products. The company’s latest single-chip terahertz radar with the highest bandwidth in the industry is a 120GHz radar chip with a 25GHz bandwidth and a 300GHz radar chip with a 40GHz bandwidth, which increases the range resolution to 3-6 mm. In China, Microchip has launched a CMOS terahertz radar chip with a bandwidth of 13GHz and 160GHz, narrowing the technological gap at home and abroad. Terahertz radar can be widely used in various industrial, medical, and maintenance operation and maintenance scenarios, such as level/liquid level gauges that require high accuracy, environmental collision perception of production line robotic arms, high-precision positioning, and bottled depth measurement of liquid products , Non-contact and infection-free vital signs detection in the operation room, DNA analysis, UAV flaw detection sensors, etc.

Terahertz Imaging System

This field is mainly divided into passive and active imaging. Passive imaging is mainly used for human body security inspection. Well-known large companies in the world include ThruVision, MC2, etc. In China, the representative of Bowei Terahertz. Due to the limitation of noise performance, silicon-based chips cannot meet the terahertz front-end requirements of such systems, but CMOS can be used to reduce costs in detectors after high-sensitivity low-noise amplifiers and low-insertion-loss switching circuits and subsequent intermediate frequency amplifiers. Unlike passive imaging that does not require a light source device, active imaging requires the system to provide a terahertz light source, which can be used in a wide range of fields, from human security inspection to industrial inspection. Since human security inspection is currently dominated by millimeter wave technology, here we focus on industrial inspection imaging. Industrial inspections are divided into scenarios, including random inspections and full inspections. The largest market comes from the full inspection market. This field has high requirements for real-time imaging, and technically requires the use of photosensitive arrays to achieve. At present, international companies that master terahertz photoreceptor array technology, such as Rigi, I2S, INO, etc., use Micro Bolometer arrays, and TeraSense uses III/V group detector arrays. The Suzhou Institute of Nanotechnology, Chinese Academy of Sciences in China has implemented a photoreceptor array chip and a real-time imaging terahertz camera using surface plasmon sensing technology. These active imaging cameras all require terahertz light sources, and mainstream light sources generally use terahertz quantum cascade lasers (QCL), laser-driven terahertz radiation sources, echo oscillators (BWO) or III/V solid-state circuit frequency doubling Link implementation, the cost is generally high. Silicon-based chip terahertz sources and imaging arrays have gradually moved from academia to commercial use over the past decade, radiating power up to the milliwatt level. The earliest light source and photosensitive array based on CMOS chips were commercialized by TicWave in Germany; Alcatera brought this technology to full inspection of industrial production lines. At present, only Taijing Technology has used CMOS integrated circuits to realize the terahertz light source and photoreceptor array at the same time, which has reached the international leading level. Zion Market Research believes that terahertz imaging will contribute major market growth in several major market segments.

In terms of imaging, there is also a subdivision field of terahertz scanning microscopy, which is based on the non-contact scanning of nano- or micro-scale probes on the surface of the object to be measured, and the measurement of disturbances in the near field of terahertz to achieve imaging. The resolution mainly depends on pressing The size of the probe tip. This type of imaging system breaks through the limitation of wavelength on imaging resolution, and is very suitable for biological cell analysis, semiconductor process quality inspection and other scenarios. However, the current domestic and foreign equipment uses single-needle scanning, and the imaging speed is slow. It takes about 10 to 20 minutes of scanning time per 1 square centimeter of area, which cannot meet the needs of industrial scenarios. Such systems generally use a terahertz time-domain pulse source with a thermal radiation sensor (Bolometer), or use an expensive vector network analyzer for signal excitation and signal reception processing. In this field, silicon-based integrated circuits can greatly reduce the cost, greatly shorten the scanning and imaging time, and greatly reduce the system volume.

Terahertz Measuring Instruments

International head test instrument companies such as Keysight, Rohde & Schwarz, and Anritsu have extended microwave test instruments (vector network analyzers, spectrum analyzers, signal sources, etc.) to the terahertz frequency band. The spread spectrum modules of these companies come from upstream Module manufacturers, such as Virginia Diodes Inc, Radiometer Physics GmbH, OML, etc. The terahertz test equipment independently developed by CLP Instruments in China has reached an international level. The most landmark product is the vector network analysis and measurement system with a frequency of over 500GHz. The terahertz frequency expansion module launched by a start-up company has a great advantage in cost performance. This type of equipment is realized with a waveguide structure, which is large in size and high in cost. The main customers are universities, research institutes, large enterprises or shared platforms in high-tech development zones. Most small and micro enterprises mainly rely on leasing, and long-term rent is a huge expense. Silicon-based integrated circuits can play a role in the field of portable or low-cost measurement equipment within 200GHz in the future, and are expected to fill this market segment.

Terahertz communication system

At present, TeraPhysics is currently engaged in the research and development of terahertz communication-related products internationally, while in China, only the internal pre-research departments of universities or large companies are carrying out related research. Due to the overall noise degradation due to the large bandwidth of the communication link, silicon-based transceivers are used in combination with III/V power amplifiers and low-noise amplifiers to achieve a balance between performance and cost. If 6G communication uses terahertz for micro-base station data interconnection, the annual market size of silicon-based terahertz communication integrated circuits can reach at least several billion US dollars.

　　2. The rise of silicon-based terahertz integrated circuit companies

After more than ten years of international academic exploration and the continuous improvement of the process performance of major wafer manufacturers, silicon-based terahertz integrated circuits have entered the stage of mass production. From the current SiGe and CMOS process performance, silicon-based integrated circuits can be competent for signal amplification within 200GHz, frequency multiplication, frequency mixing, frequency locking, phase locking and wave detection within 600GHz. These are the basic functional modules for realizing terahertz signal transmission and reception. Among them, the output power of the amplifier within 200GHz is about 10mW, the noise figure is not worse than 15dB, and the bandwidth can be tens to hundreds of GHz; the detection NEP is in the order of 100pW/Hz1/2 and so on. These series of properties can make a big difference in each of the above areas.

International terahertz technology companies based on silicon-based chip technology have made good progress. Germany’s Silicon Radar provides the industry’s highest bandwidth SiGe radar chip and has completed 3 rounds of financing, including government and commercial venture capital; France’s TiHive completed 8.6 million euros of financing in 2020, specializing in the development of high-speed terahertz CMOS cameras; Germany’s TicWave It is the first in the industry to provide real-time terahertz imaging CMOS chip solutions; Alcatera in the United States has launched the industry’s first real-time terahertz imaging equipment for full inspection of disposable hygiene products (diapers, sanitary napkins) production lines, and has received orders from international leading customers; The domestic microchip has completed A round of tens of millions of financing; the start-up company Taijing Technology has used CMOS technology to achieve terahertz light sources and imaging chips with frequencies close to 400GHz in less than a year after its establishment, and will soon launch real-time for industrial production lines. High-speed terahertz imaging device.

　　3. The impact of silicon-based chips on the scale of the terahertz industry

BCC Market Research predicts that the global terahertz market will reach $908.6M ($908.6 million) in 2024 and $3.5B ($3.5 billion) in 2029. This market report is based on the statistics, analysis and forecast of mainstream terahertz technologies (such as optoelectronic technology, Bolometer, etc.) and related products, and does not take into account the profound impact of solid-state circuits, especially silicon-based integrated circuits, on the industry. Just as the realization of radio frequency signal transmission and reception by CMOS technology has promoted the large-scale popularization of mobile phones, the realization of millimeter wave signal transmission and reception by SiGe or CMOS has accelerated the mass production of automotive millimeter wave radar. Promote the transformation of terahertz technology to the huge civilian market.

　4. Summary

There are many subdivisions of terahertz applications, and the annual market size of each subdivision ranges from tens of millions to hundreds of millions. The design of silicon-based chips should first fully understand the needs and pain points of the application market, and fully plan for versatility and compatibility to meet the diverse needs of system integration.

When silicon-based chips became possible, the era of terahertz civilian use really came.