ITO target material Recycling

Introduction to ITO Target Material

1. Basic Composition and Core Properties

• Chemical Composition: Based on indium oxide (In₂O₃) as the matrix, doped with 5%-10% (molar ratio) tin oxide (SnO₂). Tin ions (Sn⁴⁺) replace some indium ions (In³⁺) to form free electrons, endowing the material with conductivity; the cubic bixbyite structure of indium oxide ensures high visible light transmittance.
• Key Physical Properties:
  • Density: Must reach over 95% of the theoretical density (ideally 98%-99%) to avoid “particulate” defects caused by internal pores during sputtering, which would affect film quality.
  • Purity: Industrial-grade targets are typically 99.99% (4N), while high-end applications (e.g., semiconductors) require 99.999% (5N). Impurities such as alkali metals and heavy metals are strictly controlled (content <1ppm) to prevent increased film resistivity.
  • Microstructure: Uniform grains (5-20μm in size) and no segregation ensure consistency in sputtering rate and film performance.
  • Mechanical Properties: Flexural strength >150MPa and hardness >500HV to meet mechanical stability during sputtering (preventing target cracking).

2. Manufacturing Process: Key Transformation from Target Powder to Target Material

1. Powder Pretreatment:
   The target powder must have controlled particle size (1-5μm), specific surface area (>10m²/g), and particle size distribution (D50 <3μm). Uniform mixing is achieved via ball milling or air jet milling to avoid compositional segregation during subsequent sintering.
2. Forming:
   • Small targets: Dry pressing (pressure 100-300MPa);
   • Large/irregular targets (e.g., 1.5m-grade targets for G10.5 displays): Cold isostatic pressing (CIP, pressure 200-400MPa) to ensure uniform green body density (>65% of theoretical density).
3. Sintering:
   • Atmosphere: Sintered in oxygen or air (to inhibit In₂O₃ decomposition);
   • Temperature and Time: Held at 1400-1600℃ for 10-20 hours. Particle bonding and pore elimination occur via diffusion sintering;
   • Innovative Processes: Microwave sintering (shortening time to 2-4 hours) and spark plasma sintering (SPS, low-temperature rapid densification) improve efficiency but with higher costs.
4. Post-Processing:
   After cutting, grinding (surface roughness Ra <0.5μm), and bonding (welding to copper/molybdenum backing plates for enhanced heat dissipation), the final targets are ready for direct installation in sputtering equipment.

3. Classification and Application Scenarios

• Planar Targets: Simple structure, suitable for small-to-medium area film deposition (e.g., mobile phone screens, small-sized photovoltaic cells), but with low utilization (only 30%-40%).
• Rotary Targets: Tubular in shape, enabling uniform sputtering via rotation, with utilization increased to 60%-80%. They are mainstream for large-area, high-production scenarios (e.g., 8K TV panels, G8.5+ display production lines).

1. Display Sector: Pixel electrodes in LCD/OLED panels and conductive layers in touch screens, requiring film transmittance >90% and resistivity <10⁻⁴Ω·cm.
2. Photovoltaic Industry: Front/back transparent electrodes in heterojunction (HJT) solar cells, balancing high transmittance (especially in the near-infrared region) and low contact resistance.
3. Functional Coatings: Smart glass (electrochromic), electromagnetic shielding films, and sensor electrodes, relying on target stability and film uniformity.

4. Performance Requirements and Quality Control

• Sputtering Stability: Target composition uniformity error must be <0.5%; otherwise, film resistivity fluctuations (>5%) may occur.
• Impurity Control: Alkali metal (Na, K) content <0.1ppm to prevent ion migration in films at high temperatures; carbon and hydrogen impurities can cause “black ash” defects during sputtering.
• Dimensional Accuracy: Straightness error of large rotary targets <0.1mm/m to ensure uniform gaps with sputtering equipment (affecting film thickness deviation).

5. Market Landscape and Challenges

• Market Size: The global ITO target market was ~$4.5 billion in 2023, projected to reach $6.8 billion by 2028, with China accounting for over 50% (mainly for display panels).
• Key Enterprises:
  • Japan: JX Nippon Mining & Metals (high-end targets, semiconductor-grade), Sumitomo Metal;
  • China: Xian Dao Rare Materials (global leading rotary target production capacity), Hengtong Optic-Electric (G10.5-grade large-size targets);
  • South Korea: Samsung SDI (supporting local display industry chains).
• Critical Challenges:
  • Indium Resource Constraints: Global indium reserves are only ~50,000 tons, with indium accounting for >70% of target costs. Price fluctuations ($300-400/kg in 2023-2025) affect industry stability.
  • Competition from Alternatives: AZO (aluminum-doped zinc oxide), silver nanowires, and graphene aim to replace ITO but still lag in comprehensive performance (transmittance + conductivity + stability).
  • Large-Scale and Thin-Substrate Trends: G11 display panels (3370×2940mm) require targets over 3m in length, and sintering thin targets (thickness <5mm) is significantly more challenging.

6. Future Trends

1. High Density and Low Defects: Sintering with nano-target powder (particle size <100nm) to achieve target density >99%, reducing film particulate defects.
2. Recycling and Circular Utilization: Over 90% of indium can be recovered from retired targets via acid dissolution and purification. Global indium recycling accounted for 35% in 2025, projected to reach 50% by 2030.
3. Composite Targets: Doping with gallium (Ga), zinc (Zn), etc., to optimize ITO film weather resistance (e.g., anti-high-temperature yellowing) for flexible display needs.

Summary