New Waveguides for Microwave Monolithic Integrated Circuits Using Distributed Parameter Effects of Semiconductor Carriers

随着微细光刻有源半导体器件的小型化，由于无源电路对衬底面积的要求越来越大，目前单片微波集成电路的集成度受到了限制。它们形成在具有外延表面层的半绝缘化合物半导体衬底(GaAs和InP)上，由于半导体载流子的分布参数效应，它们表现出显著的慢波传播。这种波导可以减小分布参数无源电路的尺寸。此外，它们的传输特性可以通过偏压来改变，这为电调谐和有趣的非线性相互作用提供了可能。建立了MIS和肖特基共面波导的基本设计原则，并采用等效电路的方法对其传输特性进行了理论分析。推导了传输特性与频率和偏置关系的解析表达式。利用分子束外延(MBE)在GaAs和InP半绝缘衬底上形成了GaAs和InGaAs表面半导体层。结果表明，GaAs肖特基型共面波导具有慢波传播特性，其传输特性包括频率和偏置特性与理论预测吻合良好，费米能级钉扎的控制对于具有偏置调谐能力的MIS共面波导的实际开发具有重要意义。提出了一种新的利用超薄分子束外延硅层的钝化技术，该技术在InP衬底上得到了非常有前途的InGaAsMIS结构，没有任何费米能级钉扎迹象。

The integration level of monolithic microwave integrated circuits (MMICs)is presently limited owing to large substrate area requirements for passive circuitry in spite of the advanced miniaturization of active semiconductor devices with fine-line lithography.In the present study, MIS (metal-insulator-semiconductor) and Schottky coplanar waveguides for application to MMICs are investigated theoretically and experimentally. They are formed on semi-insulating compound semiconductor substrates ( GaAs and InP) with epitaxial surface layers, and show remarkable slow-wave propagation due to distributed parameter effects of semiconductor carriers. Such waveguides can reduce the size of distributed parameter passive circuits. Additionally, their transmission properties can be altered by electrical bias, opening up the possibility of electrical tuning and of interesting non-linear interactions.Basic design principles of MIS and Schottky coplanar waveguides were established and an theoretical analysis of transmission properties was made, using an equivalent circuit approach.Analytical expressions on frequency and bias dependences of transmission properties were derived.Molecular beam epitaxy (MBE) was used to form GaAs and InGaAs surface semiconducting layers on GaAs and InP semi-insulating substrates. The GaAs Schottky-type coplanar waveguides showed slow-wave propagation, and their transmission properties including frequency and bias dependences, were found to be in good agreement with the theoretical prediction.Control of Fermi level pinning is obviously extremely important for practical exploitation of MIS coplanar waveguides with bias tuning capability. A novel passivation technique using an ultra-thin MBE silicon layer was developed, and it resulted in a very promising InGaAs MIS structures on InP without any indication of Fermi level pinning.