Silicon Germanium Technology: Low Cost GHz Performance
Insights | 02-09-2025 | By Gary Elinoff
Key Takeaways about Silicon Germanium Technology – Low Cost meets GHz Speeds:
- Silicon Germanium (SiGe) chips feature the powerful, critical ability to combine high-frequency elements and ordinary CMOS digital logic on the same monolithic chip.
- New technologies are enabling 5G to reach its full mmWave potential.
- The lower cost of SiGe chips is relevant for a range of applications beyond smartphones.
Introduction
Silicon Germanium (SiGe) transistors will make it easier and less expensive to exploit the gigahertz-level frequencies that are the heart of the emerging world of automotive radar and 5G. And it’s not just their low cost that’s raising eyebrows. As described by Analog Devices[1], “Silicon germanium (SiGe) is a semiconductor technology made for wireless applications. It offers the high-speed, high-frequency performance needed for wireless systems, and it provides the potential for integrating analog, RF, and digital functions on a single integrated circuit (IC). Plus, it is based on low-cost Si wafers.”
SiGe semiconductors are capable of producing RF outputs of between 0.5 and 1.0 watts at frequencies of up to 20 to 30 GHz. That, and the ability to combine high frequency elements and digital logic on the same monolithic chips makes them a key technology for 5G handsets and other diverse system on a chip (SOC) designs.
However, designers need to be aware that SiGe chips and transistors can’t handle as much power as Gallium Nitride (GaN) or Silicon Carbide (SiC). Additionally, thermal conductivity is low, rendering SiGe devices unsuitable for high-power amplifier designs.
The Challenge of 5G
5G’s frequency allotments range up to as high as 47 GHz. And yet, most consumers ’ phones only use “Low Band”, in the 2 GHz range. Basically, very similar to the frequencies employed by “old School” 4G
5G Spectrum: Image source: 5G Store
In a previous Electropages article, the questionable utility of the “High Bands” for most consumers was explored. However, in that article, the benefits of Mid Band and High Band can be a true boon for certain commercial, industrial and military users. SiGe semiconductors will make the higher frequency mid and high bands accessible at reasonable price points. Being able to include CMOS logic functions on the same chip will also serve to make devices smaller and lower the parts count.
Additionally, using these chips for lower frequency applications allows them to deliver greater power. This will make SiGe technology valuable in many unexpected applications.
Digging Deeper into SiGe Semiconductor Technology
SiGe are heterojunction bipolar transistors (HBT), a type of bipolar junction transistor (BJT) that uses different semiconductor materials for the emitter and base regions, creating a heterojunction. The HBT improves on the BJT in that it can handle signals of very high frequencies, up to several hundred GHz.
5G Semiconductors offer excellent noise characteristics, and they are good performers at very low temperatures. These characteristics make them well suited for space based applications, as well as in quantum computing readout circuitry. Additionally, these HBTs perform well in space based radioactive environments, offering relatively high resistance to single-event effects (SEE) and to total ionizing dose (TID).
Another important characteristic is that designers can adjust germanium content during epitaxial growth during fabrication. This allows optimization for varying combinations of speed, power, and gain as needed for any type of use case.
SiGe Semiconductor Technology is Widely Available
Of critical importance SiGe is a mature technology and already supports multiple use cases in millimeter wave systems and in RF applications. There is a large design ecosystem as well as an established supply chain. Of critical importance, Infineon, GlobalFoundries and IBM all have established foundry support for this technology.
A summary is provided below that contrasts and compares the advantages and disadvantages of Silicon Germanium with other key semiconductor technologies.
| Property | SiGe | GaN | Ga₂O₃ (Gallium Oxide) | SiC | GaAs |
|---|---|---|---|---|---|
| Electron Mobility (cm²/V·s) | Medium (≈1500) | High (≈1500–2000) | Low (≈300) | Medium (≈900) | High (≈8500) |
| Bandgap (eV) | ~1.1–1.6 (adjustable) | 3.4 | 4.8–5.3 (very wide) | 3.2 | 1.43 |
| Breakdown Field (MV/cm) | ~1 | 3.3 | 8–10 (very high) | 3 | 0.4 |
| Thermal Conductivity (W/cm·K) | ~0.15 | 1.3–2.3 | 0.1–0.3 | 3–4.9 | 0.5 |
| Saturation Velocity (cm/s) | 1×10⁷ | 2.5×10⁷ | ~2×10⁷ | 2×10⁷ | 1×10⁷ |
| Radiation Hardness | Good | Excellent | Excellent | Excellent | Moderate |
| Max Frequency (fT, GHz) | >300 GHz | ~100–300 GHz | Experimental | ~50–150 GHz | ~250 GHz |
| Power Handling | Moderate | Very High | Extremely High (in theory) | Very High | Moderate |
| Integration with CMOS | Excellent (BiCMOS) | Poor | Very Poor | Poor | Moderate |
| Maturity / Availability | High (commercial) | High (commercial) | Low (early-stage R&D) | High (commercial) | High (mature, declining use) |
Chart provided by AI analysis
The bottom line is that SiGe can combine ultra-high, 300 GHz and better frequency elements with ordinary CMOS digital functions on the same monolithic chip. The unique advantage of SiGe is that none of the other four can match Silicon Germanium’s level of integration in a single monolithic die at a commercial and mature level.
Tower Semiconductor’s SiGe BiCMOS Terabit Platform
Devices in this platform[2] feature transistors “with speeds exceeding Ft/Fmax of 340/450GHz” (see glossary). These units are well-suited for 24 GHz and 77 GHz automotive radar and 5G mmWave use cases.
The platform also provides “low-noise transistors for use in smartphone and GPS wireless receivers and high-power transistors for use in mobile and IoT wireless transmitters.”
Additionally, the company notes units in the family feature a low noise feature of < 1.3 dB at 40 GHz. This feature made it a suitable component for a 256-transmitter-element phased array, with an output of 43 dBm (~20 watts) at 60 GHz. By way of explanation, in terms of RF, a dB (decibel) is a logarithmic term comparing a transistor’s RF output to one milliwatt.
SiGe Components for 5G
Because cell phone manufacturers typically do not publish their bills of materials, specific examples are hard to pin down. Chip manufacturers, too, can be cagy, and specifics can be hard to come by. This is understandable, as giants like IBM and the international manufacturers of smartphones are notorious for keeping their cards close to their vests.
However, the BGA9H1BN6 from Infineon is a low noise amplifier for 4G and 5G based on Silicon Germanium BiCMOS technology. It operates on midband wavelengths, and provides 20.3 dB gain and 0.6 dB noise figure at a current consumption of only 5.5 mA.
Reportedly, Infineon’s BGA10H1MN9 low noise amplifier devices are also employed in 5G smartphone RF front-ends. Members of the company’s 5G Mobile Industry Processor Interface (MIPI) LNA MMICs operate at frequencies up to 6 GHz. These units, too, are likely to be SiGe based.
SiGe – High Frequency Application where Low Cost is a Prime Factor
One of the prime areas of SiGe SOCs will have wide application in automotive technology, regardless of whether the vehicle is an EV, a hybrid or even if it’s gas-powered. And, similar to handset applications and unlike military/space applications, low cost is a must.
As pointed out by Amol Deore in his LinkedIn Article[3], “Sensors are the heart of modern automotive systems, encompassing everything from basic functionalities like temperature and pressure monitoring to advanced capabilities such as lane-change assistance and collision avoidance systems. These sophisticated devices gather and process data crucial for decision-making, ensuring both the safety and comfort of passengers.”
Other vital high-frequency automotive applications are Lidar, Radar, and, perhaps most importantly, reliable internet connectivity.
Wrapping Up
Applications, including but not limited to vehicles and smartphones face a dilemma; they must operate at GHz level speed, but they can’t afford the super-high price tags of military devices and other highly specialized use cases. Enter Silicon Germanium semiconductors.
These devices are built on low-cost, industry-standard silicon wafers. As such, it’s easy to incorporate standard CMOS digital logic on the same monolithic device. This ability will serve to lower parts count, improve reliability, and lower manufacturing costs. Additionally, decision making can often take place on- chip, with no need to access off-chip logical decision making, further enhancing functional speed.
It’s difficult to firmly state the upper speed limits of devices because speed and power are inversely proportional on specific transistors or SOCs.
The efficacy of SiGe is certainly not limited to smartphones. However, these semiconductors will make it possible for popularly priced units to access the Mid Band and mmWave frequencies already allocated to 5G that are largely left untouched at present.
Challenges and Opportunities
As always in semiconductor technology, higher speed and lower costs are paramount among the challenges and opportunities. The industry, surprisingly, has not done a good job in publicizing these devices and their game-changing potential. This is especially odd, due to their Ft (speed at which gain reduces to unity) potential of 300 GHz and above
References
- SiGe Technology Makes Practical Advances. Analog Devices
- SiGe BiCMOS Terabit Platform. Tower SemiConductor
- Driving Innovation: Unleashing the Potential of Silicon Germanium in Automotive Sensors. LinkedIn
Glossary of Terms
- Ft. frequency at which a transistor’s current gain reduces to 1
- Fmax. The frequency at which a transistor’s power gain reduces to 1
- MIPI. Mobile Industry Processor Interface
- LNA. Low Noise Amplifier
- MMIC. Monolithic Microwave Integrated Circuit
- SOC. System on a chip
