**2.3 Advantages of GaAs versus silicon in MMIC design**

Traditionally low frequency MMICs are produced on silicon substrate. Production costs of MMICs on silicon substrate are cheaper. High frequency MMICs are produced on gallium arsenide (GaAs), a III-V compound semiconductor. MMICs are compact and have low volume and area (from around 1 mm<sup>2</sup> to 10 mm2 ). MMICs can be produced in low-cost mass production. The electronic properties of GaAs are significantly better than those of silicon. GaAs has a higher electron mobility and higher saturated electron velocity than silicon. These properties allow transistors produced on GaAs to operate at frequencies higher than 0.3THz. In comparison to silicon devices, GaAs chips are less sensitive to heat because their higher bandgap. Noise of GaAs modules at high frequencies is lower considerably than the noise of silicon modules because of lower resistive device parasitic and higher carrier mobility. These features make GaAs chips and modules attractive to smartphones, cellular phones, medical communication systems, radars, and high frequency phased arrays. Gunn diodes are produced on GaAs substrate to generate RF signals. GaAs devices can be used to emit light efficiently since they have a direct band gap. Silicon devices are very poor at emitting light due to their indirect bandgap. Recent advances may make silicon lasers and LEDs possible. Si LEDs cannot emit visible light and rather work in IR range due to theirs lower bandgap. However, GaAs LEDs may function in visible red light. GaAs substrate is a good choice in high power applications for space electronics devices and optical applications. Silicon is a cheaper substrate than GaAs substrate. Silicon crystal has a significantly mechanically stable structure. Silicon can be grown to very large diameter units. Silicon modules have very high yields. Silicon modules are very attractive for design and production of very large ICs due to good thermal properties of silicon which enable very dense packing of transistors. Silicon dioxide is one of the best insulators, this is a major advantage of Silicon. Silicon dioxide can easily be used in silicon devices. Silicon dioxide layers are adherent to the underlying Silicon layer. GaAs does not have does not have stable oxide does not form a stable adherent insulating layer. An important advantage of silicon over GaAs is the higher hole mobility of silicon which allows the production of higher-speed P-channel field effect transistors. These transistors are required for CMOS logic. GaAs transistors lack a fast CMOS structure. So, GaAs logic circuits have much higher power consumption, GaAs logic cannot compete with silicon logic modules. Silicon technology has lower production cost compared with GaAs devices, contributing to a cheaper Silicon IC. Silicon wafer diameters are typically, 20 cm or 28 cm. GaAs wafer diameters are 10 cm to 15 cm. Other, Indium Phosphide (InP) III-V technologies, offers better properties than GaAs in terms of higher cutoff frequency, gain, and noise figure. InP devices are more expensive than silicon and GaAs modules. InP wafer sizes are smaller than GaAs wafers and are more fragile. Silicon Germanium technology offers higher speed transistors than conventional Silicon devices with similar cost expenses. Gallium Nitride, GaN, is used to produce power amplifiers MMICs. GaN transistors can work at much higher voltages and function at much higher temperatures than GaAs transistors, they are used to produce power amplifiers at high frequencies. Properties of dielectric substrates used in MMIC technology are given in **Table 2**.
