本論文第三章介紹一10-GHz類比式相位偏移器之設計，並用第二章所述之積體被動元件製程來製作。相位偏移器使用具磁耦合之全通網路此一電路架構來實現，由可變電容與兩耦合電感所組成；兩耦合電感間之耦合係數設計為正值，以期單級網路便可達到大的相位偏移量。由於製程良率尚不高，因此未有完整的相位偏移器可供量測；但有鐵電可變電容及耦合電感測試鍵可各別量測。量測結果顯示，鐵電可變電容於5-V偏壓下可達到2:1的可調度，0-V時的電容密度約為20 fF/µm2；上電極面積為7×7 µm2的鐵電可變電容其品質因子在10 GHz時約在8–13間。耦合電感量測得之自感於10 GHz為1.4 nH，品質因子約為14，耦合係數為0.64。我們將鐵電可變電容及扣掉下針pad的耦合電感的實際量測結果匯入電路模擬軟體以模擬相位偏移器之性能。模擬結果顯示，相移器的輸入及輸出電壓駐波比由dc至10.5 GHz皆小於2。於原始設計頻率10 GHz時，植入損耗小於5 dB，在可變電容偏壓6 V下的相位偏移量為135°；但相位偏移量最大的點為8.6 GHz，而相移量可達180°。經檢查發現，造成最大相位偏移量的頻率由原始設計的10 GHz移至8.6 GHz的原因為耦合電感之全波電磁模擬時並不準確。經重新模擬後，耦合電感的全波電磁模擬結果與量測結果則相當貼近。
;When implemented using IPD processes, the size of a microwave circuit can be effectively reduced. In this thesis, the development of an integrated passive device (IPD) process featuring ferroelectric capacitors is presented. The devices that can currently be fabricated using the IPD process we develop include ferroelectric varactors and spiral inductors. A microwave phase shifter is implemented using the developed IPD process to demonstrate its potential for fabricating tunable microwave circuits.
The detail of the proposed IPD process is articulated in Chapter 2. The proposed IPD process can be used to fabricated ferroelectric capacitors and spiral inductors. The ferroelectric capacitor is formed by the first metal layer (M1), the ferroelectric barium strontium titanate (BST) thin film, and the second metal layer (M2), whereas the spiral inductor is constructed using the third metal layer (M3), the benzocyclobutene (BCB) inter-metal dielectric layer, and the fourth metal layer (M4). The major contribution of this work is to develop the gold-electroplating procedure for the M3 and M4 layers as well as the procedures for spin-coating and etching the BCB dielectric layer. By gold plating, the thicknesses of the M3 and M4 layers can reach several µm, which would reduce the microwave loss of the spiral inductor. On the other hand, the low-k BCB layer with a thickness of several µm reduces the parasitic capacitance of the spiral inductor.
In Chapter 3, the design of a 10-GHz analog phase shifter, which will be realized using the IPD process described in Chapter 2, is shown. The magnetically coupled all-pass network (MCAPN), composed of varactors and two coupled inductors, is used as the circuit topology for the phase shifter. To achieve a large phase shift by only one section of the MCPN, the coupling coefficient of the two coupled inductors within the MCAPN is set to be positive value. Due to the low yield of the IPD process, we currently do not have a complete phase shifter for measurement. Nevertheless, testkeys of ferroelectric varactors and coupled inductors are available. The measurement results of the testkeys show that the ferroelectric varactor exhibits a tunability of 2:1 under 5-V bias and a 20- fF/µm2 capacitance density at 0 V, and the quality factor of a ferroelectric varactor with a top-electrode area of 7×7 µm2 at 10 GHz ranges from 8 to 13. The measured self-inductance, quality factor, and coupling coefficient of the coupled inductors are 1.4 nH, 14, and 0.64, respectively, at 10 GHz. The measurement results of the ferroelectric varactors and the deembeded inductors are used for simulating the performances of the designed phase shifter. Simulation results show that the input and output voltage standing wave ratios (VSWRs) of the phase shifter are less than 2 from dc to 10.5 GHz. At 10 GHz, which is the original design frequency, the insertion loss is less than 5 dB and the phase shift is 135° when the varactors are biased up to 6 V. However, maximum phase shift, which is 180, occurs at 8.6 GHz. After investigation, it is found that the reason for the frequency shift is due to the inaccurate full-wave electromagnetic (em) simulation of the coupled inductors. After re-simulation, the em simulation result of the coupled inductors now closely matches the measured result.
In this work, an IPD process featuring ferroelectric varactors is successfully developed and used for fabricating ferroelectric varactors and coupled spiral inductors. Using the measured results of the fabricated ferroelectric varactors and coupled inductors to simulate the performance of a microwave phase shifter, it is demonstrated that the IPD process proposed in this thesis has the potential for fabricating tunable microwave circuits.