In high-end industries such as optoelectronic technology, semiconductor manufacturing, and precision optics, hard optical substrates are core basic materials that directly determine the performance ceiling, stability, and application scenarios of devices. Among them, quartz, sapphire, and silicon wafers have become the three most mainstream and widely used hard optical substrates in the current market, covering the entire industrial chain from consumer electronics and automotive displays to aerospace, military industry, and semiconductor chips. This article systematically analyzes the core characteristics and differentiated advantages of the three types of substrates, and provides references for selection, R&D and industrial layout in related fields.
1. Quartz Substrate: Benchmark for UV Transmittance and Thermal Stability
Quartz substrates are mainly made of fused silica (main component SiO₂), and are the preferred material for scenarios requiring high wave transmission performance and thermal stability in the field of precision optics. Its core advantages stem from its unique amorphous glassy structure, which avoids lattice defects of crystalline materials, thus exhibiting excellent optical and thermal properties.
In terms of optical performance, quartz substrates have an ultra-wide transmission range of 185nm–2100nm, especially a transmittance of more than 85% in the deep ultraviolet (DUV) band (<300nm) and over 92% in the visible light band, with no fluorescent background interference. This feature makes it irreplaceable in scenarios such as DUV lithography, fluorescence microscopes, and high-power laser windows. In terms of thermal performance, the thermal expansion coefficient of quartz is as low as 0.5×10⁻⁶/℃, the best among the three substrates, which can withstand high temperatures above 1000℃ and has extremely strong thermal shock resistance, maintaining surface accuracy unchanged in extreme environments with drastic temperature changes.
In terms of mechanical and chemical properties, quartz has a Mohs hardness of 7, and its surface can be easily polished to sub-nanometer roughness (Ra<0.5nm), with excellent resistance to strong acids and alkalis and superior chemical stability. Typical applications of quartz substrates are concentrated in high-end precision optical fields, including DUV lithography equipment, aerospace optical sensors, precision optical prisms, and laser nuclear fusion devices. In addition, in the field of chip manufacturing, quartz is also an important carrier of dielectric substrates, which can improve the electron mobility and heat dissipation performance of chips with hexagonal boron nitride modification technology.
2. Sapphire Substrate: Performance Leader in Extreme Environments
Sapphire substrates are mainly composed of α-alumina (α-Al₂O₃), a single crystal material of hexagonal crystal system. With its extremely high hardness, excellent chemical inertness and wide-band wave transmission performance, it has become the core substrate choice for optical devices in extreme environments, and also a key material in fields such as LEDs and consumer electronics.
Mechanical performance is the most prominent advantage of sapphire substrates—its Mohs hardness is as high as 9, second only to diamond, with extremely strong scratch resistance, wear resistance, impact resistance and pressure resistance, making it an ideal material for consumer electronic components such as mobile phone lens covers and smart watch dials. In terms of optical performance, the transmission range of sapphire covers 200nm–5500nm, including ultraviolet, visible light and mid-infrared bands, among which the high transmittance in the UVC ultraviolet band gives it unique advantages in scenarios such as ultraviolet detection and sterilization equipment.
In terms of thermal and chemical properties, sapphire has a melting point of 2053℃ and a thermal conductivity of about 40W/(m·K), which can maintain stable optical and mechanical properties in high-temperature environments; at the same time, it has extremely strong chemical inertness, which can resist corrosion by most acids and alkalis, adapting to extreme working conditions such as aerospace and military industry. China has become the world's largest producer and consumer of sapphire substrates, with enterprises such as Tiantong Co., Ltd., Weilan Lithium Core and Or瑞德 forming a complete industrial layout. In addition to consumer electronics and LED fields, the application of
sapphire substrates also extends to high-end fields such as aerospace and high-voltage equipment.
3. Silicon Wafer Substrate: Cost-Effective Choice for Semiconductors and Infrared Optics
Silicon wafer substrates are mainly made of single crystal silicon (Si), the most mature and lowest-cost category among the three substrates. With their excellent infrared wave transmission performance and semiconductor properties, they have become core basic materials in the fields of infrared optics and semiconductor devices, covering multiple industrial chain links such as semiconductor chips, infrared imaging, and lidar.
In terms of optical performance, the core advantage of silicon wafers is concentrated in the infrared band—it is opaque in the visible light band, but has excellent transmittance in the 1.2μm–7μm infrared band, with a high refractive index of about 3.45 and no obvious absorption, making it an ideal substrate material for devices such as infrared thermal imagers, infrared sensors, and lidar windows. In terms of thermal and electrical properties, the thermal conductivity of silicon wafers is about 150W/(m·K), much higher than that of quartz and sapphire, with good thermal conductivity; at the same time, it has typical semiconductor properties, which can realize conductive performance regulation through doping and is highly compatible with semiconductor manufacturing processes.
In terms of mechanical performance and cost, the Mohs hardness of silicon wafers is 6.5, lower than that of quartz and sapphire, but thanks to the mature wafer processing technology, it has low difficulty in large-size processing and high yield, and its cost is much lower than the previous two types of substrates. The industrialization of silicon wafers has entered the large-size iteration stage, and the localization process of 12-inch silicon wafers is accelerating. The application scenarios of
silicon wafer substrates are highly concentrated in the fields of semiconductors and infrared optics.
4. Core Differences and Selection Guide of the Three Substrates
The core differences of the three types of hard optical substrates (
quartz, sapphire, and
silicon wafers) are concentrated in optical transmission range, mechanical strength, thermal characteristics, processing difficulty and cost. The specific selection needs to be comprehensively judged based on scenario requirements, performance requirements and cost budget.
The core advantages of quartz are high DUV transmittance, ultra-low thermal expansion coefficient and extremely high surface accuracy, suitable for high-end precision optical scenarios; sapphire is suitable for consumer electronics, aerospace, military industry, LEDs and other scenarios requiring high wear resistance and corrosion resistance; silicon wafers are suitable for large-scale application scenarios such as semiconductor manufacturing, infrared imaging and lidar, with infrared high transmittance, semiconductor compatibility and high cost performance.
5. Industry Development Trends and Outlook
With the rapid development of emerging fields such as optoelectronic technology, semiconductor industry and AR/VR, the hard optical substrate industry is ushering in a new round of technological iteration and market expansion. Globally, the market size of optical hard films and related substrate materials is growing continuously, and it is expected to exceed 21.5 billion US dollars by 2030, with the Asia-Pacific region becoming the main engine of global growth.
In terms of technological development, the three types of substrates all show a development trend of "large size, high precision and multi-function". The rise of emerging fields has brought new growth opportunities for hard optical substrates. In the future, with the continuous breakthrough of technology and the continuous upgrading of industrial demand, the three types of substrates will develop in a more accurate, efficient and cost-effective direction, and the localization substitution process will continue to accelerate, providing core support for the independent controllability of China's optoelectronic and semiconductor industries.
