In this thesis, broadband compact digital and variable InP/InGaAs PIN attenuators using a multi-layer MMIC technology have been proposed and demonstrated, which are implemented by using the III-V semiconductor fabrication facility in KAIST.
In high-frequency communication systems, PIN diodes are key components in achieving switching and variable resistance functions. PIN diodes have shown higher performances such as high switching rates, low-insertion loss, high isolation and high power handling capabilities. Among various kinds of PIN diodes for high frequency applications, InP/InGaAs PIN diodes have material-related excellent properties, such as high electron mobility, low turn-on voltage, high cutoff frequency and compatibility with InP-based HBTs for high frequency applications.
In this work, InP/InGaAs PIN diode and passive devices such as MIM capacitors and thin film resistors were fabricated and characterized to construct a device library for PIN MMICs. The fabricated InP/InGaAs PIN diode showed a 1.4 Ω on-resistance with a 22 fF off-capacitance, which correspond to the switching cutoff frequency of 5.17 THz. A 480 Å NiCr layer was evaporated to form thin-film resistors with a sheet resistance of 25.43 $\Omega/\Box$ and a 2000 Å SiNx dielectric layer was deposited to make MIM capacitors with a capacitance value of 238 $pF/mm^2$.
On the basis of the device library, digital and variable attenuator circuits were designed, simulated and analyzed. In digital attenuators, an improved design which reduces the parasitic inductance and broadens the operating frequency band was proposed and simulated. The proposed digital and variable attenuators were fabricated by using a benzocyclobutene (BCB)-based multi-layer MMIC technology. The multi-layer structure and meandered thin film resistor line configuration effectively reduce the chip area of the digital and variable attenuators. The fabricated 3-bit, 4-bit, 5-bit digital MMIC attenuators demonstrated low insertion loss of $3.9\sim7.2$ dB and high return loss of $8.6\sim10$ dB. Especially, improved digital attenuators showed broader frequency operation and better input/output return losses compared to the conventional digital attenuators. Variable attenuators which have Pi and T network configurations also demonstrated low insertion loss of $1.5\sim1.6$ dB with return loss of $7\sim8.5$ dB, and low DC power consumption of $20\sim34$ mW for Ku/K/Ka broadband operation. The performances obtained in this work indicate that the proposed digital and variable attenuators using InP/InGaAs PIN diodes are applicable to compact and broadband MMIC components.
본 논문에서는 광대역의 집적화된 digital/variable InP/InGaAs PIN attenuator를 다층구조 MMIC 공정기술로 제작하였다. PIN diode의 높은 switching rate와 low insertion loss, high isolation, high power handling capability를 이용하고 InP/InGaAs 물질을 사용하여 높은 전자이동도 낮은 turn-on voltage, 높은 cutoff frequency, InP-based HBT와의 capatibility를 이점으로 활용하여 InP/InGaAs PIN attenuator MMIC를 제작하였다. 제작된 InP/InGaAs PIN diode의 cutoff frequency는 5.17THz로 높은 주파수 특성을 보였고 1.4Ω의 on-resistance와 22 fF의 off-capacitance를 가졌다.
Device library를 바탕으로 하여 digital / variable attenuator를 각각 design하고 simulation하였다. digital attenuator에서는 주파수 대역을 높이고 attenuation 특성을 높인 설계를 제안하였다. 제작된 attenuator MMIC는 낮은 insertion loss와 우수한 matching 특성을 보였으며 다층구조 공정으로 매우 낮은 면적을 가짐을 알 수 있었다. 이로써 다층구조의 InP/InGaAs PIN attenuaotr는 저면적, 광대역 MMIC에 응용됨을 알 수있다.
