An evaluation of the immunity characteristics of an LSI with capacitors embedded in an interposer

Abstract

To improve the electrical characteristics of LSIs, we are developing technology for embedding chip capacitors into interposers for LSIs. In this paper, we applied an interposer with embedded capacitors to an image-processing LSI and compared its electrical characteristics with that of a conventional LSI. We confirmed improvements in the timing margin, signal integrity, and immunity characteristics of the LSI. I. INTRODUCTIONPower supply voltages of LSIs are falling, since the manufacturing process for LSIs is progressing toward ultrafine. As a result, very small fluctuations in the power supply voltage cause the LSI to malfunction, making power integrity (hereinafter PI) a severe and growing problem [1]- [3].On the other hand, we need to supply high-frequency currents to LSIs to maintain their performance. We generally use bypass capacitors, which are placed near the LSI on the PCB (printed circuit board) as shown in Fig. 1, as highfrequency current sources. When the operating frequency of an LSI exceeds several hundred MHz, the LSI needs very high frequency currents of over 1 GHz. This makes it impossible to ignore the small inductances between the power supply pins of the LSI and the bypass capacitors, such as via holes, since high-frequency currents cause the power supply voltage to fluctuate in proportion to these inductances. Therefore, to maintain the desired performance of LSIs at higher clock frequencies, we will need to reduce the inductances in the power distribution network to be able to reduce fluctuations in the power supply voltage.We are currently developing the embedded technology of chip capacitors into interposers for LSIs. Using this technique, the distance between the power supply pins of the LSI and the bypass capacitors can be minimized and the inductances between them reduced. There have been numerous studies on embedded technology [4]- [7]. In these references, it is mainly reported that the impedance of power distribution network can be improved by embedding capacitors into the PCB. However, the question of LSI performance has not been examined in these studies.In this study, we applied an interposer with embedded capacitors to an image-processing LSI for digital televisions (Fig. 2) and evaluated the LSI's electrical characteristics.