1、 Introduction: Data is the blood of the digital age, so the light module is the "heart" that allows blood to flow at high speed. It is not large in size, but it plays a crucial role. It can convert the electrical signals generated by servers and switches into optical signals, and transmit them at high speed through thin fiber optic cables. It is the core component for achieving high-speed network interconnection. From the Internet and 5G network we use every day, to the huge data center supporting the AI revolution, to the future autonomous driving and the meta universe, we can't do without countless light modules working behind our backs. However, while this "heart" is running at high speed, a silent "temperature war" has already begun: the heat generated by the internal laser chip suddenly increases, and temperature fluctuations of ± 0.1 ℃ are enough to cause wavelength drift and signal distortion, restricting its performance and reliability. Precision thermal management has evolved from an auxiliary technology to a key bottleneck determining the evolution of optical communication systems. On the battlefield of temperature control at the micrometer scale, micro thermoelectric coolers (MicroTEC) are becoming the key "thermal control chips" to break through with their fast and accurate temperature control capabilities. Image source: TTS (Tucker Thermal System) With the upgrading of global data centers towards higher speeds and larger capacities, as well as the explosive growth in demand for artificial intelligence training and inference, high-speed optical modules are rapidly iterating towards higher rates such as 400G, 800G, and 1.6T. The components stacked on circuit boards are becoming increasingly dense, generating more and more heat, making thermal management a common challenge for various electronic devices. With the rapid development from high-speed optical modules to AI chips, the MicroTEC market for temperature control in electronic devices is huge and has broad prospects. So today, let's talk about the application and challenges of MicroTEC in the field of thermal management of optical modules! 
2、 What is MicroTEC thermal management black technology? 
To understand what MicroTEC is, a thermal management black technology, let's first review the knowledge of semiconductor coolers (TECs). Semiconductor cooler (TEC), also known as thermoelectric cooler or electronic cooler, is a solid-state heat pump device based on the Peltier effect. It is mainly composed of N-type and P-type bismuth telluride semiconductor materials, and the direction of heat flow is controlled by direct current to achieve cold end heat absorption and hot end heat absorption. The cooling/heating function can be switched by changing the direction of current. Image source: TTS (Tucker Thermal System) After understanding the general principle of TEC semiconductor refrigeration chips, let's take a look at its internal structure. There are many closed loop combinations of N-type and P-type semiconductors inside. The raw material for N-type and P-type semiconductors is generally bismuth telluride (Bi2Te3), which is also a widely used thermoelectric material; Encapsulated by two white ceramic substrates, the ceramic substrate is usually made of aluminum oxide and aluminum nitride, but the cost is much higher than that of aluminum oxide. In addition, the ceramic substrate will be metalized, usually plated with copper, nickel, gold, etc; The surrounding area is sealed with thermally conductive and insulating interface materials; Finally, two wires were connected at both ends to make our TEC semiconductor refrigeration chip. Of course, the editor is only briefly introducing the basic internal structure, and there are many key processes involved in the preparation, which will not be elaborated here. In fact, the most essential thing inside is bismuth telluride, a thermoelectric material, and the entire thermoelectric effect relies on it to generate. High quality semiconductor refrigeration chip manufacturers basically buy their own raw materials to make crystal rods, and the key technology lies in the preparation and wire cutting processing of the crystal rods. The higher the purity and crystal quality of the crystal rods, the more precise the wire cutting process, and the better the TEC effect produced. At present, bismuth telluride crystal rods are still relatively well made in Russia, with an import price of about 2000 yuan per kilogram. There are also products made domestically, but the quality is still relatively poor, and of course, the price is relatively lower. So many TEC manufacturers in China directly import bismuth telluride crystal rods from Russia and then make wire cutting to produce finished TECs. 
And MicroTEC is a miniature TEC, with a size usually ≤ 3mm × 3mm (which is the size of the rice grains we eat), a grain size<0.35mm × 0.35mm, and a minimum grain size of 0.15 mm × 0.15 mm. Therefore, MicroTEC is a miniaturized, highly accurate, and highly integrated TEC semiconductor refrigeration chip, and is an absolute star product of TEC semiconductor refrigeration chips. 
3、 Technical difficulties and challenges in the preparation of MicroTEC: 1. Challenges at the thermoelectric material level: (1) Significant material scale effects: Commercial Micro TEC uses Bi ₂ Te ∝ based thermoelectric materials, but traditional testing uses millimeter scale samples (such as 2 × 2 × 8 mm ³), while the size of Micro TEC thermoelectric arms has been reduced to 150 × 150 × 200 μ m ³ (see Ju Technology data). The uniformity and thermoelectric properties (such as ZT value) of materials at the micrometer scale are difficult to guarantee, and there is a lack of standard testing methods. 
(2) Poor mechanical properties and low processing yield: Bi ₂ Te ∝ has a layered crystal structure and is prone to cleavage along the c-plane, resulting in a high rate of slice damage, especially when cutting<0.5 mm chips, resulting in extremely low yield. The poor axial/radial uniformity of crystal bars produced by traditional zone melting method further limits miniaturization. 
(3) Material preparation process bottleneck: ① Zone melting method: suitable for large-sized but difficult to meet Micro TEC's requirements for high uniformity and high strength. ② Although new processes such as powder metallurgy/hot extrusion can achieve a minimum of 50 μ m thermoelectric arm (Zhongke Bosheng), the process is complex and costly, and has not yet been widely popularized. 2. Difficulties in the manufacturing process of microdevices using bismuth telluride chips: (1) High precision positioning and assembly: ① It is necessary to accurately arrange p/n-type thermoelectric grains (size<0.35 × 0.35 × 0.4 mm) in a p-n-p-n alternating sequence on a ceramic substrate. ② The positioning accuracy requirement is<5 μ m (see Torch Technology), and the mounting deviation should be ≤ 2 °; The pad spacing is only about 0.1 mm, which places extremely high demands on the equipment. 
(2) Strict welding process control: ① Adopting a "sandwich" double-sided welding structure (clamping the thermoelectric arm with upper and lower ceramic substrates), it is necessary to prevent grain displacement or inversion during the welding process. ② Solder paste needs to have low solid content and high wettability to reduce the increase in interface resistance and failure caused by residual flux. ③ The porosity of solder joints needs to be extremely low, and the grain size of solder needs to be refined to enhance mechanical properties and diffusion resistance. 
(3) Consistency and yield challenges: ① A single Micro TEC contains 8-100 pairs of thermoelectric pairs, and any grain defect can cause the entire device to fail. ② Most domestic enterprises lack experience in full process quality control, making it difficult to achieve high yield mass production. 
3. Limitations of equipment and testing system: (1) High end equipment relies on imports: key equipment such as high-precision surface mount machines and tape machines have a unit price of millions of yuan and a slow speed (only a few thousand pieces/hour), making it difficult to meet the needs of efficient mass production. 
(2) Insufficient detection capability: Systematic testing is required for each production process (such as temperature cycling, mechanical strength, aging, Δ Tmax/Qc max, etc.), but there is a lack of supporting automated testing equipment and standards in China. 
4、 MicroTEC is applied in thermal management of optical modules. High speed optical modules have high integration and local power consumption, and traditional passive heat dissipation is difficult to meet the requirements. Micro TEC provides active, local, and highly responsive thermal management solutions. The mainstream thermal management solution for optical module TOSA is Micro TEC, which has a package size as small as 1.5 × 1.1 × 0.65mm and a heat pump density of 43W/cm ², suitable for compact packages such as QSFP-DD/OSFP. (2) Integrated packaging: TEC and TO tube shells are fused, increasing heat dissipation efficiency by 30-40% and reducing assembly gaps and thermal resistance. (3) Composite heat dissipation: ceramic substrate microchannel+heat pipe/phase change material, with a thermal resistance as low as 0.05 ℃/W, enhancing heat dissipation at the hot end. 
Micro TEC is mainly placed inside the TOSA (Light Emitting Assembly) of the optical module and connected to the laser diode tube assembly through a thermal interface material to control its heat generation. The wavelength temperature coefficient of DFB/EML and other lasers is about 0.1 nm/° C, and the drift within the commercial temperature range (0-70 ° C) can reach 7 nm, which easily exceeds the channel spacing of WDM systems. Micro TEC can control the temperature drift within ± 0.1 ° C. (1) Temperature control requirement: The wavelength of the laser is extremely sensitive to temperature (drift 0.1-0.2nm per ℃), and the high-speed optical module (400G+/800G/1.6T) needs to stabilize the temperature at ± 0.01- ± 0.1 ℃ to suppress drift and reduce error rate. This is a necessary condition for cloud vendor certification, and the penetration rate in data communication scenarios is 100%. (2) Application objects: Mainly used for thermal sensitive devices such as laser diodes (LDs), EML chips, detectors, etc., directly stabilizing junction temperature through chip mounting and PID closed-loop control. (3) Performance gain: In the 400G module, TEC can improve wavelength stability by more than 30%, reduce bit error rate to ≤ 1e-8, and ensure high-speed long-distance transmission. 
5、 MicroTEC's Market and Future Prospects in Thermal Management of Optical Modules 
1. Scale and Growth: (1) The Micro TEC market for optical modules is expected to reach approximately 6.6 billion yuan by 2024; Approximately 5.5 billion yuan in 2025, expected to exceed 10 billion yuan in 2031, with a CAGR of over 12%. 
(2) Speed upgrade driver usage increase: 2-4 pieces are required for 400G, approximately 1.5-2 pieces for 800G, and 2.5-4 pieces for 1.6T, doubling the value of a single module TEC. 2. Competitive landscape (1) Japan US dominance: Ferrotec (Yamato Thermomagnetic) and KELK (Komatsu) from Japan account for over 80% of the high-end market, while Tucker Thermal Systems (formerly Laird from the United States) and Phononic account for 15%. 
(2) Domestic breakthrough: Fuxin Technology (IDM mode, ZT value 1.3-1.45, monthly production of 600000 pieces) has achieved 400G/800G batch supply with significant cost advantages. 3. Domestic alternative drivers: High end Micro TECs are in short supply, and domestic optical module manufacturers (such as Zhongji Xuchuang and Xinyisheng) are accelerating the certification of domestic devices, which is a dual benefit of policies and costs. 
Representative manufacturers of Micro TEC: Ferrotec (Daiwa Thermomagnetic), KELK (Komatsu), Tucker Thermal Systems (formerly Laird, USA), Fuxin Technology, Jianju Technology, Hubei Segre, Wuhan Xinsaier, Arctic Ocean, Hongchang Electronics, etc. (For manufacturers not mentioned, please feel free to share in the comment section) 
6、 Summary image source: TTS (Tucker Thermal System) Micro TEC is the core requirement for high-speed optical module thermal management. The explosion of AI computing power has accelerated the penetration of 800G/1.6T, driving the price and quantity of Micro TEC to rise; Although high-end Micro TECs are still monopolized by foreign giants, domestic manufacturers are gradually breaking through in materials, processes, and costs, and there is a vast space for substitution. We believe that in the future, domestic TEC manufacturers will also reap a big market dividend in the field of optical modules!