Atomic Diffusion Bonding for Optical Devices with High Optical Density

Abstract

An inorganic bonding method providing 100% light transmittance at the bonded interface was proposed for fabricating devices with high optical density. First, we fabricated 5000 nm-thick SiO2 oxide underlayers on synthetic quartz glass wafers. After the film surfaces were polished to reduce surface roughness, the wafers with oxide underlayers were bonded using thin Ti films in vacuum at room temperature as a usual atomic diffusion process. After post annealing at 300 °C, 100% light transmittance at the bonded interface with the surface free energy at the bonded interface greater than 2 J/m2 was achieved. Dissociated oxygen from oxide layers probably enhanced Ti films oxidation, resulting in high light transmittance with high bonding strength attributable to the annealing. Using this bonding process, we fabricated a polarizing beam splitter and demonstrated that this bonding process is useful to fabricate devices with high optical density.

Surface-activated direct bonding of diamond (100) and c-plane sapphire with high transparency for quantum applications

“…The interfaces touch each other completely, illustrating that the intermediate layer is deformed to fit the undulating diamond surface. The crystallinity of the intermediate layer is clarified based on TEM observations aligned to the and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) directions of the sapphire. No crystal structure is observed in the intermediate layer.…”

“…Alternatively, dry process-based bonding is a possible choice for bonding diamond (100) to mother substrates. Atomic diffusion bonding (ADB) [10][11][12][13][14][15][16][17] and surface activation bonding (SAB) 7,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] have been reported for various material combinations. ADB is a promising technique for some applications and can ensure chemical bond formation by atom diffusion.…”

Atomic diffusion bonding with oxide underlayers using Al and amorphous Si films for high optical density applications

“…9) To overcome this difficulty, we proposed ADB using oxide underlayers. 19) Figure 1 portrays a schematic illustration of this method. For this method, oxide underlayers are deposited on two wafer's surfaces, then the wafers are bonded using ADB with thin metal films in vacuum at room temperature as a usual atomic diffusion process.…”

“…20) In fact, 100% light transmittance and surface free energy of the bonded interface of more than 2 J m −2 were achieved. [19][20][21] Herein, 100% light transmittance indicates that the loss of optical power at the bonded interface is less than the detection limit. The IAD method, a widely used technique for formulating optical thin films, 22) can be used for bonding interfaces with optical thin films such as dielectric multilayers.…”

Atomic diffusion bonding using oxide underlayers for optical applications

“…To resolve this difficulty, we propose ADB using oxide underlayers to provide 100% light transmittance at the bonded interface. 20) Here, 100% light transmittance means that loss of optical power at the bonded interface is lower than a detection limit. Figure 1 provides the process scheme of ADB with oxide underlayers and post-bonded annealing process.…”