Emerging applications in the RF/microwave/ millimeter wave regimes require miniaturization, portability, cost and performance as key driving forces in this evolution. Multi-band applications are also becoming extremely important within passive development to realize multiple frequency bands for various wireless and optical sub-carrier multiplexing (OSCM) systems. Investigations on System on Package approach for module development [1] have become a primary focus due to the real estate efficiency, cost-saving and performance improvement potentially involved in this integral functionality.
In most of the presently used microwave integrated circuit technologies, it is difficult to integrate the passives efficiently while maintaining the desired performance. Another critical obstacle in efforts to reduce the module size is the design of passive components, which occupy the highest percentage of integrated circuit and circuit board real estate. Design flexibility and optimized
integration can be achieved with multilayer substrate technology in which free vertical real-estate is taken advantage of. Various highly intergrable multilayer technologies such as multilayer low-temperature co-fired ceramic (LTCC) [2]-[3] and multilayer organic (MLO)
[4]- [5] are thus being studied to achieve complete System on Package solutions.
II. MULTILAYER INDUCTORS
High Qs at the frequency range of interest can be obtained by designing CPW inductors and HGP [9] series and cascade inductors using multilayer organic technology. The CPW spiral inductor, Fig. 1, avoids via losses, has reduced dielectric losses and increased SRF. The advantage of the HGP implementation includes shunt parasitic capacitance eddy current reduction resulting in
higher Q. Fig. 2 shows a measured Q of 182, SRF 20GHz, effective inductance (Leff) of 2 nH. The series inductor is designed as one continuous turn; however, the turn on the second layer is offset from the turn on the top layer. This offset helps decrease the parasitic capacitance
between the turns and improves SRF. The top metal and bottom metal of the cascade inductor spiral separately and are connected at the center of the spiral. Both inductors are illustrated in Fig. 3. The top and bottom spiral are overlapped and strongly coupled yielding an impressive Q
and effective inductance, Leff. The Q, L and SRF of the HGP series and cascade inductors are 122, 2.5nH, 10GHz and 165, 3.4nH, and 11.5GHz, respectively, Fig 4. Another benefit of the HGP configuration is that the Leff can be adjusted by increasing or decreasing the shunt
parasitic capacitance due to the ground plane. This is achieved by decreasing or increasing the hollow, respectively.
III. EMBEDDED FILTERS
Several front-end RF filters were designed in various topologies. Two LPF were designed for 750MHz and C band, respectively; two BPF were designed for C GHz and Ku bands, respectively. For RF and low microwave applications, this filter can be implemented by combinations of capacitive and inductive lumped passive components. Fig. 5 shows the 2 nd order Bessel lumped element lowpass filter with cutoff frequency at 750MHz.
The simulated and measured return loss and insertion loss are shown in Fig, 6. It is used to filter 1Gb/s header data stream in a 10Gb/s OSCM system operating at 14GHz. A stepped impedance LPF was designed with cutoff frequency at 7GHz, Fig. 7 . It is used to filter 10Gb/s data stream in a 14GHz OSCM transmitter as well. The series inductors represent the high impedance sections(94? ) and the shunt capacitance represent the low impedance sections(7.2? ). The return and insertion loss are shown in Fig. 8.
The first bandpass filter design for C band applications consists of a square patch resonator[10] with inset feed lines, Fig. 9. The inset gaps act as small capacitors and cause the filter to have a pseudo-elliptic response with transmission zeros on either side of the passband. This structure also has a tunable bandwidth. The length of the insets and the distance between them are the main controlling factors, effectively setting the size of the mode-splitting perturbation in the field of the resonator. The length of the feed lines is determined by the input and output matching requirements. Fig 10 shows a center frequency of 5.8 GHz, bandwidth of 1.5 GHz and a minimum insertion loss of 3 dB.
The second BPF desi gn for Ku band applications uses a broadside-coupled microstrip dual-mode square ring resonator[11]. This consists of a microstrip ring resonator that is perturbed by inserting a small metal polygon at one corner, Fig. 11. The outputs are taken symmetrically with respect to this perturbation, which causes the resonator modes to split into two degenerate coupled modes, giving a second-order bandpass filter response. The advantages of this design are compactness (nominal edge length is l/4) and controllability of the bandwidth by varying the size 'd' of the perturbation that causes mode splitting. Larger perturbations cause more mode splitting and result in a larger bandwidth. The strength of the capacitive coupling also controls the bandwidth. Strong coupling lowers the external Q factor of the resonator and increases the bandwidth. Fig. 12 shows a measured center frequency of 14.5GHz, bandwidth of 1 GHz and an insertion loss of 4 dB.
IV. CONCLUSION
In this paper we have reported embedded passive inductor and filter designs and measurements for C, S, and Ku bands implemented in a multilayer organic-based packaging environment. A compact inductor with a measured Q of as high as 182 and SRF as high as 20GHz is presented. The filters demonstrate potential for compact designs in multiple filter bands.
RF-Microwave Multi-band Design Solutions for Multilayer
Organic System on Package Integrated Passives
http://shunpike.mit.edu/writings/MTT2001final.pdf
CRF_Zambrano C. Jaydi D.
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