RF performances of inductors integrated on localized p+-type porous silicon regions

Abstract

To study the influence of localized porous silicon regions on radiofrequency performances of passive devices, inductors were integrated on localized porous silicon regions, full porous silicon sheet, bulk silicon and glass substrates. In this work, a novel strong, resistant fluoropolymer mask is introduced to localize the porous silicon on the silicon wafer. Then, the quality factors and resonant frequencies obtained with the different substrates are presented. A first comparison is done between the performances of inductors integrated on same-thickness localized and full porous silicon sheet layers. The effect of the silicon regions in the decrease of performances of localized porous silicon is discussed. Then, the study shows that the localized porous silicon substrate significantly reduces losses in comparison with high-resistivity silicon or highly doped silicon bulks. These results are promising for the integration of both passive and active devices on the same silicon/porous silicon hybrid substrate.

Porous silicon for electrical isolation in radio frequency devices: A review

“…This observation is also valid in the case of a Selectively Grown Porous Silicon (SGPS) process where the porous silicon layer is etched from the backside. 28 In the case of localized porous silicon regions, the effects of the surrounding bulk silicon were also clearly demonstrated by Capelle and coworkers 92 for highly doped p-type silicon. To understand the effect of the localized PS substrate on the increase of losses, a simplified electric model of an inductor integrated on this substrate was suggested by the authors (Figure 19).…”

“…But, whatever the thickness of the porous silicon layer, the authors demonstrate that the performance of the RF devices is clearly reduced but is still acceptable compared to bulk silicon wafers. 92 The inductor design also has a strong influence on the losses for a given PS layer. Generally, a higher inductor area, due to an increasing number of turns, for example, leads to performance degradation.…”

Monolithic integration of low-pass filters with ESD protections on p + silicon/porous silicon substrates

“…To overcome this drawback, the RF lossy components can be integrated on insulating porous silicon (PS) substrates [4][5][6][7]. Indeed, the increase of performances of inductors, transmission lines and filters integrated on PS have been already reported [8][9][10]. In this context, the silicon/porous silicon mixed substrate becomes a serious alternative to silicon for the monolithic integration of RF circuits [11].…”

Optimized plasma-polymerized fluoropolymer mask for local porous silicon formation

“…However, for many of the above mentioned applications, it is essential to form PS in predefined regions. [4][5][6][7][8][9][10][11] Synthesis of patterned PS is usually achieved by masking a silicon substrate with a layer of etching resistant material. 12 For a short-duration anodic etching, conventional masking layers, such as photoresist 13 and silicon dioxide, 14 are quite convenient, and the corresponding masking procedures are well mastered in the semiconductor industry.…”