Research On Methods To Improve The Quality Factor Of Spiral Inductor Based On Silicon

Nowadays,wireless telecommunication system is becoming more and more popular in our daily life.Mobile phone,blue tooth and wireless local area network make our communication much more convenient than before.All of these wireless telecommunication system work in the frequency range of several hundred to several giga Hz. Traditional transmitter is comprised of discreted circuits,and its shortage is high power and big volume.CMOS with its feature dimention of 90nm and frequency of over ten GHz,for its high integration and low cost ,will take the place of expensive GaAs and become the best choice for RFIC(Radio Frequency Integrated Circuit) . Planar spiral inductor is one of the key elements of RFIC,and it exists in many modules and also can have notable influence on the performance of the cuicirt.However,because of the relatively high conductivity of the Si substrate, the quality factor(Q) of inductor is low when the frequency is as high as several GHz.So it is really difficult for inductor which is integrated on low resistance substrate to have good performance.After lots of investigation and analyzing the loss mechanisms, in order to get higher Q factor,I have finished a lot of experiments and simulations.Generally,these researches can be diveded into three aspects:first, to process the substrate,and make the substrate become high resistance.According to our test data,the Q factor of inductor can reach as high as 22 on SiO₂ while only 7 on low resistance substrate.This method is not easy,what is more,it needs extra high cost;second, to optimize the layout of the coil and this method doesn't need other expense,so it atttacts much attetion now;third, to optimize of dielectrical layer between metal and substrate.This paper did the reseach from these three aspects.Because of the limits of the process level and time,I just fabricated and tested some inductors,but I simulated a lot.This paper get the influence of some parameters of the indutor to its Q factor,and it is applicable to design inductors.This paper put forward a new structure of spiral indutor,and its feature is relatively higher Q factor and its inductance is stable, the simulation plot shows its Q factor is 30% higher than traditional inductors with fixed width and space at most,and this paper also put forward one kind of nonplanar inductor, which can lower both approximity effect and substrate loss.