Page 289 - System on Package_ Miniaturization of the Entire System

Radio Fr equency System-on-Package (RF SOP) 263

PACKAGING package • Nano-scale
• 10–20% System
IC

• 80–90% System
Connectors
• Milli-scale
Board
Discrete

• Low functional density
• Bulky
• Costly
• Low reliability

FIGURE 5.2 Packaging is the barrier to future RF systems.

showing the trend from a discrete component-based system such as the cell phone to
more convergent and miniaturized systems capable of performing a variety of functions
including, but not limited to, wireless phone, wireless networking, navigation systems,
and sensor systems [1–3].
The barriers to achieving these ultraminiaturized systems with dozens of functions
are not in the digital or CMOS silicon but in the system packaging area, as shown in
Figure 5.2. RF systems utilize passive components for matching, tuning, filtering, and
biasing. For example, a mobile phone is composed of only about 6 to 10 active
components but as many as 400 to 600 passive components, depending upon the level
of system integration. These passive components currently are all surface-mount
devices (SMDs), which account for more than 90 percent of the system components and
occupy more than 80 percent of the system board area [4]. The SOP enables reduction in
size of this non-CMOS part of the RF system by a factor of a thousand as the RF
components are miniaturized from their current thick-film-based milliscale to thin-
film-based microscale technologies. Since this non-CMOS part of the system is about
80 percent of the total size of the system and 70 percent of the cost of the system, the
SOP dramatically improves both the size and cost. If, in the future, these non-CMOS
components are further miniaturized to nanoscale, RF systems can be further
miniaturized by another factor of a thousand, leading to the possibility of megafunction
systems in the same size scale as today’s handsets.
Figure 5.3 shows an RF communication system where the SOP concept can be
implemented to enhance performance and reduce size. In the baseband section, the
major functions, such as the microprocessor, DSP, static random access memory (SRAM),
and flash, are based on silicon technology, and their progress is in line with the
advancements in SOC from 65 to 22 nm and 3D integration technologies that use
through-silicon vias for chip stacking. However, in the RF front-end section, the situation
becomes more challenging. The RF system requires unique components, such as filters,
low-loss power amplifiers, and high linearity RF switches [5]. CMOS is excellent for
baseband but is not an optimal platform for the RF front end. Here, the SOP offers a
solution that cannot be achieved either by SOC or traditional SIP technologies. In simple