In this thesis, a new Heterostructure MOS (MOSH) RF switch device was proposed and fabricated. The MOSH structure has advantages of MOS structure (very low DC current). For the first time, the MOSH structure RF switches were fabricated by using conventional GaAs-based pHEMT epi-structure and GaAs wet oxidation - LPCEO technology. Two MOSH capacitors, which consist of the RF switch device, were formed by the GaAs wet oxidation technology on the top of GaAs pHEMT structure. By the low sheet channel resistance of the high density two-dimensional electron gas (2-DEG) between the InGaP barrier layer and the InGaAs channel layer of GaAs-based pHEMT epi-structure, the two MOSH capacitors were connected back-to-back. In this study, two different types of MOSH RF switches (D-MOSH & S-MOSH) were fabricated and measured at 2 GHz. For the double MOSH (D-MOSH) structure, insertion loss and isolation performances were estimated by simulation. Then, insertion loss and isolation performances of the fabricated devices were measured in various dimension of D-MOSH structure (oxidation thickness, electrode length, electrode distance). For the other single MOSH (S-MOSH) structure, insertion loss and isolation performances of the fabricated devices were measured, which were designed to have the optimal structure dimension (thin oxidation thickness, long electrode length, narrow electrode distance) of D-MOSH devices study.
From the measurement at 2 GHz, the best switch performances of insertion loss and isolation of D-MOSH structure were obtained to be –2.7 dB and – 21.8 dB, respectively. The best switch performances of S-MOSH structure were measured to be –1.38 dB of insertion loss and –23 dB of isolation. The S-MOSH structure RF switch device showed the better switch performances than the D-MOSH switch devices.
By further optimization of oxidation thickness and device dimension, the GaAs MOSH structure is expected to show much better switch performances than the results obtained and discussed in this study.
Radar System의 구성 요소인 transmitter/receiver system, phase shifter, wireless communication 등의 block에서 switch 는 중요한 요소 중 하나이다. 따라서 switch 소자 및 이를 이용한 switch 회로의 연구가 많이 이루어져 왔고, 현재에도 활발하게 연구되고 있다. 새롭게 제안된 Heterostructure MOS (MOSH) 구조는 switch 회로에서 이용되기 위한 소자로는 최초로 제안된 구조로서, HEMT 구조에 oxidation 기술을 적용함으로써, Metal-Oxide-Semiconductor Heterojunction을 형성하기 때문에 붙여진 이름으로, 1~3 GHz 대역에서 좋은 switch 특성이 기대되는 구조이다. 기존의 RF 대역 HEMT 기반 Switch 소자는 Drain-Source 사이의 DC current에 의한 DC power 소모가 존재하였다. 본 연구에서는 DC power 소모를 줄이기 위해, 새롭게 제안된 MOSH 구조를 최초로 GaAs 기반의 pHEMT 구조에 적용하여, 이 MOSH 구조를 이용한 GaAs RF switch 소자를 제안하고, SILVACO simulation을 통해 여러 dimension에서의 소자의 특성을 예측,이를 ADS simulation을 통해 실제 1-3 GHz 주파수 대역에서의 switch 특성을 확인한 후, 최적화된 dimension을 찾아 소자를 제작하였다. Oxide는 wet 방식의 LPCEO 기술로 형성하여 소자를 제작하였다. 이 MOSH switch 소자는 2 GHz 대역에서 - 1.38 dB의 insertion loss와 -23 dB의 isolation 의 충분한 switch 특성을 보임과 함께, 다른 switch 소자들에 비해 DC power 소모가 수 μW 수준으로 매우 적음을 보였다.
