Semiconductor and Device Technology III-V Semiconductors Informational

What is the difference between GaN on SiC and GaN on Si substrates for RF applications?

Q: Which substrate should I choose for a 5G mmWave PA?

For a 5G mmWave phased array PA: per-element output power is typically < 0.5 W (+27 dBm EIRP achieved through beamforming gain from 64-256 elements). At this low power level: GaN on Si is thermally adequate (the temperature rise is manageable). The cost advantage of GaN on Si (5-20× cheaper per die) is significant when multiplied by 256 elements per base station. However: GaN on SiC provides higher PAE (25-35% vs 20-30% for Si), which reduces the total DC power consumption of the array. The system-level choice depends on: total cost of ownership (including thermal management cost saved by higher efficiency) vs die cost. Currently: the market is split between GaN on SiC (Qorvo, MACOM) and SiGe/CMOS solutions (Qualcomm, Analog Devices) for mmWave gNB. GaN on Si for mmWave is emerging.

Q: Can GaN on Si match GaN on SiC power levels?

Not at the same die size. The thermal limitation of Si caps the power density at 2-3 W/mm. To deliver the same total output power: use a larger die (more gate periphery at lower power per mm). A 100 W PA: GaN on SiC uses approximately 10 mm gate periphery at 10 W/mm. GaN on Si would need 30-50 mm gate periphery at 2-3 W/mm (3-5× larger die). The Si substrate is much cheaper per mm², so the larger die may still cost less. However: the larger die occupies more package area and may not fit in constrained form factors (phased arrays, portable equipment).

Q: What is the reliability difference between substrates?

At the same junction temperature: the reliability of GaN on SiC and GaN on Si is comparable (MTTF is primarily determined by T_j, not the substrate). The difference: GaN on SiC runs at a lower T_j for the same power dissipation (because SiC removes heat faster). Lower T_j → longer MTTF (exponential relationship from Arrhenius). Example: for a fixed 4 W dissipation: GaN on SiC: T_j = 150°C → MTTF > 10⁷ hours. GaN on Si: T_j = 200°C → MTTF ≈ 10⁶ hours (10× shorter). To get the same MTTF on Si: derate the power (use only 2 W → T_j = 150°C → same MTTF). This derating effectively cuts the usable output power by 50%. For long-life applications (telecom: 20+ years): GaN on SiC is strongly preferred due to the thermal reliability advantage.

GaN on SiC and GaN on Si represent two different substrate approaches for GaN RF transistors, and the difference between them impacts performance, cost, and reliability: (1) Thermal conductivity difference: SiC substrate thermal conductivity: k = 490 W/m·K (excellent heat spreading). Si substrate thermal conductivity: k = 150 W/m·K (3.3× worse than SiC). The thermal difference between substrates is the most important distinction. For a PA dissipating 4 W on a 1 mm² die: GaN on SiC: junction temperature rise ΔT_j ≈ 30-40°C above the package base. GaN on Si: ΔT_j ≈ 90-120°C above the package base (3× higher). The higher junction temperature on Si reduces: maximum output power (the PA must be derated), efficiency (gain and PAE degrade), and reliability (MTTF decreases exponentially). (2) RF performance difference between substrates: at the same junction temperature: the RF performance is similar (the GaN epitaxial quality is comparable on both substrates for modern processes). The practical difference: GaN on SiC can deliver 2-3× higher power density (5-12 W/mm vs 2-3 W/mm for Si) before hitting the junction temperature limit. (3) Cost difference: SiC substrates: $2,000-$5,000 per 4-inch wafer (expensive). Si substrates: $50-$100 per 8-inch wafer (inexpensive). Cost per mm² of die: GaN on Si is 5-20× cheaper than GaN on SiC. (4) Applications for each: GaN on SiC: dominant for high-power RF applications (base stations with 10-100+ W PAs, radar, electronic warfare, satellite). The thermal advantage is essential for these continuous-duty, high-power applications. GaN on Si: emerging for lower-power RF applications (< 10 W per device): 5G mmWave FEM (per-element power < 0.5 W), Wi-Fi 6E/7 FEM (1-3 W output), consumer LNA and switch applications (low power, cost-sensitive).

Category: Semiconductor and Device Technology

Updated: April 2026

Product Tie-In: Transistors, MMICs, Evaluation Boards

GaN Substrate Comparison for RF

The difference between GaN on SiC and GaN on Si is fundamentally a thermal vs cost tradeoff. The substrate material determines the heat removal capability and the die cost.

Common Questions

Frequently Asked Questions

Which substrate should I choose for a 5G mmWave PA?

For a 5G mmWave phased array PA: per-element output power is typically < 0.5 W (+27 dBm EIRP achieved through beamforming gain from 64-256 elements). At this low power level: GaN on Si is thermally adequate (the temperature rise is manageable). The cost advantage of GaN on Si (5-20× cheaper per die) is significant when multiplied by 256 elements per base station. However: GaN on SiC provides higher PAE (25-35% vs 20-30% for Si), which reduces the total DC power consumption of the array. The system-level choice depends on: total cost of ownership (including thermal management cost saved by higher efficiency) vs die cost. Currently: the market is split between GaN on SiC (Qorvo, MACOM) and SiGe/CMOS solutions (Qualcomm, Analog Devices) for mmWave gNB. GaN on Si for mmWave is emerging.

Can GaN on Si match GaN on SiC power levels?

Not at the same die size. The thermal limitation of Si caps the power density at 2-3 W/mm. To deliver the same total output power: use a larger die (more gate periphery at lower power per mm). A 100 W PA: GaN on SiC uses approximately 10 mm gate periphery at 10 W/mm. GaN on Si would need 30-50 mm gate periphery at 2-3 W/mm (3-5× larger die). The Si substrate is much cheaper per mm², so the larger die may still cost less. However: the larger die occupies more package area and may not fit in constrained form factors (phased arrays, portable equipment).

What is the reliability difference between substrates?

At the same junction temperature: the reliability of GaN on SiC and GaN on Si is comparable (MTTF is primarily determined by T_j, not the substrate). The difference: GaN on SiC runs at a lower T_j for the same power dissipation (because SiC removes heat faster). Lower T_j → longer MTTF (exponential relationship from Arrhenius). Example: for a fixed 4 W dissipation: GaN on SiC: T_j = 150°C → MTTF > 10⁷ hours. GaN on Si: T_j = 200°C → MTTF ≈ 10⁶ hours (10× shorter). To get the same MTTF on Si: derate the power (use only 2 W → T_j = 150°C → same MTTF). This derating effectively cuts the usable output power by 50%. For long-life applications (telecom: 20+ years): GaN on SiC is strongly preferred due to the thermal reliability advantage.

Keep Reading

What is the difference between GaN on SiC and GaN on Si substrates for RF applications?

GaN Substrate Comparison for RF

Frequently Asked Questions

Which substrate should I choose for a 5G mmWave PA?

Can GaN on Si match GaN on SiC power levels?

What is the reliability difference between substrates?

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