Which transistor technologies are used in RF?
RF systems use several semiconductor technologies, chosen by frequency, power, noise, integration and cost. CMOS and SOI dominate highly integrated transceivers and switches; SiGe HBT offers high fT with BiCMOS integration; GaAs pHEMT and HBT serve LNAs and handset PAs; GaN HEMT provides high power density and breakdown for base-station, radar and satellite PAs; LDMOS remains common for high-power sub-4 GHz base-station and industrial amplifiers; InP reaches the highest frequencies.[1][2]
How do they compare?
| Technology | Strengths | Typical uses |
|---|---|---|
| Bulk CMOS / FinFET | Integration, digital, cost | Wi-Fi, Bluetooth, cellular transceivers, mmWave beamformers |
| RF SOI | Low-loss switches, stacking | Antenna switches, tuners, front-end modules |
| SiGe HBT/BiCMOS | High fT/fmax, low noise | Automotive radar, mmWave, LNAs |
| GaAs pHEMT | Low noise, good switches | LNAs, discrete amplifiers |
| GaAs HBT | Single supply, efficiency | Handset PAs |
| GaN HEMT | High breakdown, power density | Base stations, radar, satellite, EW |
| LDMOS | Rugged, high power, cost | Sub-4 GHz base stations, broadcast, ISM heating |
| InP HEMT/HBT | Highest frequency, lowest noise | Sub-THz, cryogenic LNAs |
What figures of merit compare transistors?
fT (unity current gain), fmax (unity unilateral power gain), NFmin, breakdown voltage, power density (W/mm of gate periphery), and thermal conductivity of the substrate (GaN-on-SiC conducts heat well).[3]
How do you choose?
Start from power and frequency, then integration needs. A single-chip IoT radio uses CMOS; a 100 W, 3.5 GHz base-station PA uses GaN or LDMOS; a 77 GHz radar uses SiGe or CMOS; a cryogenic radio-astronomy LNA uses InP.
Frequently asked questions
Why is GaN popular?
High breakdown voltage and power density allow high output power with manageable impedances.
Can CMOS do mmWave?
Yes; CMOS beamformers and radar sensors operate at 28, 39, 60 and 77 GHz.
What is f_T?
The frequency at which the transistor's short-circuit current gain falls to one.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “RF Microelectronics, 2nd ed.”. B. Razavi, Prentice Hall. 2012.
- “RF Power Amplifiers for Wireless Communications, 2nd ed.”. S. C. Cripps, Artech House. 2006.
- “The Design of CMOS Radio-Frequency Integrated Circuits, 2nd ed.”. T. H. Lee, Cambridge University Press. 2004.