Technological development
             Because of the physical characteristics of HBT such as high linearity, good broadband response, high breakdown voltage, high gain, high efficiency, low parasitic effects, design without negative bias, low phase noise, etc., cause its function with good power magnification, low standby current consumption, small size and other characteristics, it is in line with the development trend of mobile phone products, HBT has become the mainstream technology of mobile phones and wireless local area network (WLAN) power amplifier (Power Amplifiers, PA) markets. In 1995, there was only 10% of the mobile phone that using PA with HBT material, by 2005, HBT material had already penetrated over 90% into the mobile phone PA market.
On the other hand, with higher performance and technology upgrade of the mobile phones, the nature of information transmitted through the mobile phone is also becoming more diverse, with a large transmission capacity, consumer require better transmission quality, speed and battery life, and these are derived from the demand for the number of PA, the same technology evolution also occur in the Wi-Fi. In the period of the 2.4 GHz technical specification, GaAs and Si, SiGe were the available materials, but when specifications move to higher frequency (2.4 GHz / 5 GHz), only the GaAs material are qualified under the requirements of high frequency communications features and functions.
Because the end product requires different function and characteristics, there are two different materials for HBT: GaAs HBT and InGaP HBT, there is also a special characteristic of product requirement such as High Voltage HBT. Compared InGaP HBT with AlGaAs HBT, InGaP HBT has higher selective chemical wet-etching so the process yield is higher and the radio base junction valence band discontinuity, ΔEv is more, therefore, the gain at high temperature has smaller decrease, plus advantages of the smaller conduction band discontinuity, ΔEc and lower surface recombination velocity, etc, it has gradually replaced the AlGaAs HBT technology.
            Compare AlGaAs PHEMT with the conventional HEMT, there are advantages such as higher density on a two-dimensional electron gas, 2DEG, higher electron mobility, μn, relatively flat broad-plateau extrinsic transconductance), higher breakdown voltage, higher current drive capability, low leakage current, good temperature performance and better noise performance, etc., It occupies an important position to the high power base station, low-noise amplifier (LNA) and RF switch (RF Switch). Because InGaAs join PHEMT, it is specially suitable for the application of RF Switch on the computer, the application makes it the future between the computer and the computer wireless LAN (Wireless Local Area Network, WLAN), fixed long-distance wireless transmission to the wireless local loop (Wireless Local Loop, WLL), and even fiber optic communications, satellite communications, point to point microwave communications, satellite broadcasting, cable TV, digital TV applications, automobile radar and vehicle collision avoidance system and other applications that have considerable room for growth. The early mobile phone had silicon diode (Si diode) based RF switch, but in recent years due to the increase of quality requirements of 3G mobile phones, and the chip size need to be smaller, fortunately PHEMT is in line with this demand, so PHEMT is gradually replacing the Si diode applications in the mobile phone RF Switch; on the other hand, both molecular beam epitaxy (MBE) and MOCVD technologies can be produced PHEMT, traditionally, consumers are more accustomed to using MBE PHEMT, however MOCVD technology capabilities, yield and cost advantages of mass production industries were gradually recognized and quality standard are comparable to MBE technology, MOCVD technology will have the opportunity to replace the MBE technology in the near future. Based on the excellent characteristics of compound semiconductor materials, it is trend to highlight in its importance in the high-tech industries (especially the wireless communication industry)

            BiHEMT design is the application of the concept of silicon in BiCMOS, but the difference is through the circuit design and process through the epitaxial growth of the InGaP HBT linear power amplifier, AlGaAs PHEMT frequency switching, AlGaAs PHEMT logic control circuit, AlGaAs PHEMT low-noise amplifier, passive components and their connections in a single GaAs integrated circuit chip. As chip integration can be improved to reduce die size, making materials and manufacturing cost reduction. BiHEMT has recently become a new trend in the GaAs microwave circuits.

            BiHEMT has more advantages compared with the early multi-chip module. Beside the module size reduction, the cost of its packaging is lower; this will greatly reduces the cost of materials. Also, because of the internal components is GaAs-based components, it can save some bias and control circuit to make it more to power. BiHEMT structure also provides design flexbility for the circuit designers, each unit of its internal componests can choose different structure to achieve better properties. For example, The chip of the single AlGaAs PHEMT structure, the electrostatic damage proteciton diode, the drawback space, but in BiHEMT structure, HBT is base-collector diode (BC diode) can be used as electrostatic damage PHEMT switch protection diode to solve the Schotty diode problem that occupied too much space.

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