New 3D printed sample holder for LEAF-2D
One of the main challenges in LEAF-2D work package three is to use Laser Induced Backwards Transfer (LIBT) to deposit 2D materials (such as graphene) onto a silicon receiver. This is to enable the use of 2D materials in silicon-photonic devices, without the complicated multi-step processes that are involved in more conventional lithographic methods. The silicon photonics device substrates will be made in multi-user batches, based on designs from the project partners at Nvidia-Mellanox. The wafers will then be “diced” (cut) into the individual device prototypes, each of which will be approximately 2.5 x 2.5 x 0.7mm. The small size of these devices means that they will be difficult to handle; and for the LIBT process to work they need to be precisely positioned (within a few microns) relative to the donor material (the graphene). Just to make it a bit more challenging, all of this precise positioning also needs to be carried out under vacuum! So, here is the design we plan to use for these experiments…
Firstly, the device prototype will be glued to a handling plate. This consists of a thin glass sheet bonded to a silicon reinforcing frame. The glass sheet has a laser-cut hole to allow access to most of the back of the device (made to order by Tecnisco). The sample holder then has the job of clamping the donor (graphene source) and the receiver (the silicon device substrate) in precisely the correct position. The sample holder uses 3D printed parts which are made using the fused deposition modelling method (with PLA filament on a Prusa i3 MK3s+). The plastic printed parts don’t actually make a vacuum seal (typical 3D printed parts are porous) instead they just provide the structural integrity, with the actual vacuum seal being made with rubber sheeting, O-rings and by a sapphire glass window which allows the laser light into the chamber. That sapphire window means that the very thin and delicate device layer in the silicon photonic chip won’t need to withstand a full atmosphere of pressure difference (as is the case with our existing chamber design where the receiver also has to act as the chamber window). We plan to test this design out over the next month and hopefully the silicon photonic device prototypes will arrive soon.