Fabrication, Internal-matching And Testing Of Radio Frequency LDMOS Power Devices

Recently, with the rapid development of civilian mobile communication andmilitary radar technologies, the transmission quality of wireless signal is high required.As a key component of the transmitter in mobile communication base stations andmilitary radars, radio frequency (RF) power amplifier directly determines thetransmission distance and quality of wireless signal. Moreover, the performance of RFpower amplifier is closely related to its core components—RF power transistors.Lateral Diffusion Metal Oxide Semiconductor (LDMOS) power device is one kindof RF power transistors developed in recent years, whose performance is superior tothe bipolar power device, and its cost is far lower than the gallium arsenide (GaAs)power device. Therefore, LDMOS has become the core amplification device inmobile communication base stations and S-band military radars, and its marketdemand is extremely huge. At present, the market of LDMOS device is almostmonopolized by foreign manufacturers. In China, the development of LDMOS isconducted only for military application. However, the development for civilian mobilecommunication is in primary stage.In this dissertation, the RF LDMOS power device suitable for civilian use inWCDMA frequency band is developed, and the key technologies of fabrication,internal-matching and testing of the device is emphasized. The whole developmentprocess of LDMOS device is shown in more details.First, based on Shanghai Huahong0.35m standard CMOS technology, the processparameters and fabrication flow of LDMOS device is designed by using SynopsysTCAD. After the fabrication of LDMOS device, the threshold voltage, breakdownvoltage and output characteristics of the device are tested by Keithley test systems andhigh-voltage probes, so as to lay the foundation for subsequent work.Secondly, the T-shaped internal-matching network is proposed to overcome thedifficulties in testing LDMOS device or design of matching networks of poweramplifier, which caused by the low input and output impedance of LDMOS transistordie. To determine the equivalent inductance of bonding wires in the T-shapedinternal-matching network, the three-dimensional electromagnetic simulator EMDSand RF circuit simulator ADS are used to model and extract the RF equivalentparameters of bonding wires. Then, the relationship between the physical parameters and the RF equivalent parameters of bonding wires are studied, providing theguidance for selection of the bonding wires in the internal-matching network.Thirdly, the impedance of the internal-matching packaged LDMOS device is testedby Load-Pull system. The test fixtures and TRL calibration kits with good calibrationresults are developed independently, which cost only about one twentieth of similarforeign products. Using these test fixtures and TRL calibration kits, the Load-PullSystem is calibrated and de-embedded. Then the impedance of LDMOS device istested successfully, meanwhile, the testing process is also given in detail.Finally, based on the load-pull test results, a class AB power amplifier is designedand fabricated, and it could serve as the standard circuit for LDMOS devicemeasurement. Then this circuit is tested by RF signal sources, vector spectrumanalyzers and other equipments. The testing results show that, at operating frequencyof2140MHz, the power amplifier has a continuous wave output power of23.5W, apower gain more than15dB, a power add efficiency (PAE) more than48%and a thirdorder intermodulation distortion below-46dBc. The overall results exhibit theexcellent performance of LDMOS device, and the correctness of the design,fabrication and testing of power amplifier.