Global Circuit Innovations, Inc.,
Keywords: diode level shifter, silicon interposer
Summary:Input level shifting from a higher voltage to a lower voltage, such as 5V to 3.3V, becomes necessary when integrating various generation integrated circuit devices and discrete components within a system. For example, current Field Programmable Gate Array (FPGA) products typically operate with I/O voltages of 3.3V, 2.5V, or even 1.8V requirements despite being incorporated into 5V systems. In many cases, the output voltages of these newer generation lower-voltage products are sufficient to drive downstream higher-voltage logic components, but maximum input voltages from other system components are limited to at most 1V above the FPGA operational voltage. In these situations, maximum input voltage levels can be no higher than 4.3V, 3.5V, or 2.8V, respectively. There are many options for level-shifting including complex integrated circuits, but in many cases, level-shifting can be reduced to a simple series of diodes to achieve proper logic levels, while eliminating the possibility for destructive damage to the downstream lower voltage inputs. Larger area Multi-Chip Modules (MCMs) can more easily accommodate discrete series diodes assembled onto routing substrates such as FR-4 or ceramic. However, silicon interposers have already been proven to withstand the high temperatures of hermetic ceramic package sealing and operation up to 400+°C. Rather than rely on a large number of MCM components requiring either soldering, or the combination of die attach and wire bonding, embedded silicon diodes can easily be incorporated into the silicon interposer with Very Large Scale Integration (VLSI) processing, reducing overall required area, assembly complexity, and cost. This paper will identify multiple system designs requiring input level shifters, the associated layout and simulation of the diode input level shifter schematic, and the manufacturing of the embedded silicon diodes within the silicon interposer. The increase in efficiency and reduction of cost will be quantified, but ultimately the benefit of the higher temperature performance and increase in high-temperature reliability will be addressed, which would be impossible with discrete component solutions.