A view from the US space shuttle Endeavour shows the right solar array deployed, 03 December 2000, … [+]
NASA VIDEO/AFP via Getty Images
Space solar cells are evolving to address next generation deployments that require higher levels of performance, reliability, manufacturing scalability and cost. Prior generations used 4” and 6” Ge wafers to fabricate these solar cells. Increasingly, the focus is on using larger diameter substrates. Materials companies like Umicore have developed 8” Germanium wafers that have been evaluated for performance, purity and manufacturing scalability. The results are promising and highlight the time-honored maxim of the semiconductor industry – continue increasing wafer size as new applications emerge. Similar to solar cells, VCSELs are entering a phase where emerging applications are likely to challenge the current manufacturing platforms that rely on 6” GaAs substrates.
Apple’s deployment of a VCSEL (Vertical Cavity Surface Emitting Laser) based, world facing LiDAR on the iPad and iPhone platforms has significant impact on other applications like automotive LiDAR. There is a fundamental difference between consumer and automotive LiDAR applications. Smart phones typically do not demand high range, Field of View (FoV) or points per second (PPS), whereas automotive applications are geared toward safety and require significantly higher levels of performance and reliability. Consequently, VCSEL arrays in consumer applications tend to be smaller (1-2 mm²), whereas VCSEL based automotive LiDAR uses ~10X larger VCSEL sizes (10-30 mm²).
VCSELs were originally developed in the early part of this century for data communication and industrial sensing applications. They offered a lower cost alternative to edge emitting lasers (EELs) which are more expensive to fabricate at a semiconductor and packaging level. For the wavelengths used (typically 8XX-9XX nm), GaAs was the appropriate choice of semiconductor materials. The volumes were low and the size of the VCSEL die was <1 mm² per product, so 4” wafers were perfectly adequate.
As high volume consumer applications like smart phones using VCSEL arrays proliferated in the 2018 timeframe, higher volumes and the larger areas of semiconductors used drove a transition to larger wafer sizes (6” GaAs wafers). This was driven by capacity and cost constraints (generally, semiconductor processing costs do not increase dramatically with wafer size, enabling lower per unit costs as wafer size …….