Figure 3. Top view of stacked package

Figure 2. Extended view of stacked package

Figure 1. The configuration of the stacked package

Stacked Package Loop Antenna for WLAN Based on IPD Manufacturing Technology

Chang-Han Lee, Tzu-Chun Tang and Ken-Huang Lin Department of electrical engineering

National Sun Yat-sen University Kaohsiung, Taiwan

kirolee20@pcs.ee.nsysu.edu.tw, a565656kimo@pcs.ee.nsysu.edu.tw and khlin@mail.nsysu.edu.tw Abstract—This paper proposes a coupled-fed loop antenna based on integrated passive device (IPD) manufacturing technology in stacked package for IEEE 802.11b/g operation. The fractal structure is applied to further reduce the size of the loop antenna in stacked package, and high resolution of the fractal structure can be achieved by taking the advantage of the IPD manufacturing technology. Therefore, the size of the proposed antenna is only 8.5×3.25 mm² over the operating band (2.4-2.484 GHz). The radiation efficiency and peak gain are better than 60% and 1 dBi, respectively, over operating band. The detailed structure of the stacked package with proposed antenna is presented.

I. INTRODUCTION System-in-package (SiP) technology has drawn a great

attention in recent years. Many active and passive components are integrated into a single package. In the development of semiconductor manufacturing technology, Moore’s Law will eventually face its limitation. To alleviate this problem, there is a trend for semiconductor process to evolve from two-dimensional (2D) to three-dimensional (3D) structure techniques. This trend of 3D structure technique occurs not only on system-on-chip (SOC), but also on system-in-package (SiP).

Although the antenna and passive components have been integrated in 3D structure by using low temperature co-fired ceramic (LTCC) technology [1]-[2]. In 3D structure there is still need to integrate the active and passive components into a single package, especially in the considerations for antenna design. IPD manufacturing technology offers the advantages of conveniently assembling the active and passive components. . However, few papers have appeared in the open literatures concerning antenna design in IPD at either 2.45 GHz or 5 GHz [3]. To the another’s knowledge, there has been no discussion about the feasibility of antenna operates at the popular 2.45 GHz band in 3D structure by using IPD manufacturing technology.

In this paper we investigate the antenna design rules in IPD manufacturing technology, and the context is arranged as follows. In Section II, the configuration of system and design of the proposed antenna using IPD manufacturing are described. The simulated results are shown in Section III. Conclusions are presented in Section IV. The simulated results were obtained using HFSS (High Frequency Structure Simulator) version 13.0.2.

II. DESIGN OF U-SHAPED COUPLED FED LOOP ANTENNA WITH FRACTAL SLOTS

A. Configuration In this paper, the proposed stacked package antenna is

formed by stacking two package devices with solder balls connected to the upper and lower package devices. This proposed antenna is designed for IEEE 802.11b/g in the stacked package with dimension of 10×10×2.9264 mm³. The antenna is designed in the upper package and the CPW (coplanar waveguide) feed line is designed in the lower package device. Therefore, this proposed antenna is less likely

978-1-4673-0462-7/12/$31.00 ©2012 Crown

Figure 5. Comparison of proposed antenna and coupled-

fed loop antenna without fractal slots

Figure 4. Cross-sectional view of stacked package

Figure 6. Simulated peak gain and antenna efficiency

to be affected by other components or traces in the lower package device.

Fig. 1 shows the configuration of the stacked package. The stacked package device is located on the corner of the system board with relative dielectric constant of 4.4 and loss tangent of 0.001. The extended view and top view of the stacked package is shown in Fig. 2 and Fig. 3. The CPW feed line and ground are set on the second IPD layer with relative dielectric constant of 3.1 and loss tangent of 0.001 and the first IPD layer with glass material of the lower package. The antenna element is set on the second IPD layer of the upper package. The larger solders balls are used to connect the antenna element and CPW feed line and support the upper package as well. On the other hand, the smaller solder balls connect RFIC. The width and the gap of CPW are 250 μm and 25 μm, respectively. The size of antenna element is 8.5×3.25 mm², and only occupies about 27.6 percent of the whole area, allowing room for other components to use. It is found that the upper IPD size will not affect the antenna performance. Therefore, further miniaturization is still possible for the proposed stacked package. The proposed antenna element is a coupled-fed loop antenna, which includes U-shaped coupled-fed portion and fractal slots portion. The gap of U-shaped coupled-fed is 20 μm. U-shaped coupled-fed portion provides capacitively coupling for impedance matching. The loop antenna is shorted to the ground of the CPW at the end of structure, and connected by larger solder balls and vias. The fractal slots are etched near the shorted end of antenna. Therefore, the impedance matching of antenna is less likely to be affected by fractal slots. As shown in Fig. 4, the antenna ground is shorted to system ground by a number of vias and bond wires.

B. Fractal technology for antenna miniaturization In some manufacturing processes, such as printed circuit board technology, it is not easy to realize the complex and fine fractal slots on loop antenna. Because the IPD manufacturing is a photolithography processing technology,

the complex fractal slots can be etched on the proposed antenna. As shown in Fig. 5, the resonant frequency of the proposed antenna is operated at 2.45 GHz, and the resonant frequency of the antenna without fractal slots is seen at 2.59 GHz. It is observed that the resonant frequency is shifted by about 140 MHz to lower frequencies by adding a number of fractal slots.

III. SIMULATED RESULTS The simulated S11 of the proposed antenna is also shown in

Fig. 5. The bandwidth of the proposed antenna is 120 MHz (S11<-10dB) at the center frequency of 2.45 GHz, also covering operating band for IEEE 802.11b/g operation. As shown in Fig. 6. The simulated efficiency and peak gain of the proposed antenna are over 60 % and 1 dBi at operating band (2.4-2.484 GHz) of proposed antenna.

IV. CONCLUSIONS An antenna-integrated stacked package with coupled-fed

loop antenna for IEEE 802.11b/g operation is proposed. By advantage of IPD manufacturing, fractal technology can be utilized to reduce the size of the antenna to form a very compact loop antenna. Therefore, the size of the proposed antenna is only 8.5×3.25 mm² over operating band (2.4-2.484 GHz). The radiation efficiency and peak gain are all better than 60% and 1dBi, respectively, over operating band respectively for IEEE 802.11b/g operation.

ACKNOWLEDGEMENT The author would like to think Advance Semiconductor

Engineering (ASE) Inc. for IPD technical support.

REFERENCES

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[2] Y. P, Zang, M. Sun, and W. Lin, “Novel antenna-in-package design in LTCC for single-chip RF transceiver,” IEEE trans. Adv. Packa., vol. 56, no. 7, pp. 2079-2088, jul. 2008.

[3] T. C. Tang, and K. H. Lin “Antenna in package design for WLAN using MCM-D manufacturing techmology,” in Proc. IEEE Antennas Propag. Soc. Int. Symp., pp 1315-1318, Jul. 2011.

[4] J. Grzyb, and G. Troster, “MM-wave microstrip patch and slot antennas on low cost large area panel MCM-D substrates-a feasibility and performance study,” IEEE trans. Adv. Packa., vol. 25, no. 3 pp 397-408, Aug. 2002.