Integration of Single‐Crystal LiNbO₃ Thin Film on Silicon by Laser Irradiation and Ion Implantation– Induced Layer Transfer

Abstract

Ferroelectric materials have found extensive application in microelectronics, microelectromechanical systems (MEMS), and electro-optic devices.[1] Ferroelectric oxides have been used in modulators, resonators, piezoelectric components, infrared-detector elements, acoustic delay lines, microwave-tunable devices, and in data processing and memory elements. The use of thin-film layers of such ferroelectric oxides can dramatically reduce device operating voltages and enable monolithic device integration. However, the integration of high-quality ferroelectric thin films in planar device architectures on silicon substrates remains a technological challenge. A promising candidate material for such thin-film integration is LiNbO 3 , a well-known nonlinear optical crystal that exhibits an extraordinary spontaneous polarization (71 lC cm -2). LiNbO 3 optical waveguides are of great importance in electro-optic applications [2,3] and could be substantially improved through a successful thin-film integration technology. Direct wafer bonding and layer-transfer techniques are promising methods for fabricating high-quality single-crystal thin films without heteroepitaxial growth and the attendant materials-defect problems associated with lattice mismatch between the thin-film layer and the silicon substrate. Implantation-induced layer transfer processes have previously been reported for the layer transfer of Si, InP, Ge, and diamond. [4,5] Recently, layer splitting and transfer of ferroelectric materials such as LiNbO 3 , LiTaO 3 , KTaO 3 , SrTiO 3 , and BaTiO 3 have also been demonstrated through a sacrificial wet etching and anodic bonding process combined with a crystal ion slicing method. [6][7][8][9][10][11] However, because of large mismatch in the coefficient of thermal expansion (CTE) between LiNbO 3 ((7.5-14.4) × 10 -6 m°C -1 , depending on cutting orientation) and Si (2.6 × 10 -6 m°C -1 ), thermal mismatch-induced stress at the LiNbO 3 /Si interface occurring during heating and cooling steps in the direct bonding and layer transfer process is quite large in comparison to other material systems. This complicates the development of layer transfer and bonding processes for the integration of LiNbO 3 on silicon.Laser lift off (LLO) and laser-induced forward transfer methods have been widely investigated as an alternative approach to the integration of PZT (Pb(Zr,Ti)O 3 ), GaN, and Si thin films. These methods employ excimer laser irradiation and an intermetallic bonding layer (PdIn) as an adhesive layer. [12][13][14] However, for the microphotonic device applications anticipated in this study, the LiNbO 3 thin film needs to be formed directly on the silicon substrate without any intermediate metallic adhesive layer.In this communication, we introduce a novel method of thin-film integration using laser-induced layer transfer in conjunction with ion implantation to integrate single-crystal LiNbO 3 thin films on silicon substrates. Figure 1 represents the overall process. Light ions such as hydrogen and helium are implanted i...

Tailorable Optical Response of Au–LiNbO3 Hybrid Metamaterial Thin Films for Optical Waveguide Applications

“…In terms of the selection of oxide dielectric materials, LiNbO 3 (LNO) has attracted great research interest in the past two decades, because of its multifunctional properties including ferroelectric, piezoelectric, pyroelectric, electro‐optics, acousto‐optical, birefringence, and nonlinear optical properties . LNO also presents enormous potentials in optical devices, such as electro‐optical and acousto‐optical modulators, actuators, second‐harmonic generators, and waveguides .…”

Toward High‐Quality Epitaxial LiNbO3 and LiTaO3 Thin Films for Acoustic and Optical Applications

“…Now a new generation of devices is emerging using thin crystals . The single‐crystal films are fabricated by means of wafer bonding and polishing or by ion implantation, wafer bonding to the host substrate, and slicing during annealing ( Figure ) . The examples of the microresonator and CMOS (Complementary Metal‐Oxide‐Semiconductor) technology compatible modulator, fabricated by these layer transfer techniques are given in Figures and , respectively.…”

“…Schematic representation of the layer transfer process by the ion slicing technique consisting of a) ion implantation, b) wafer bonding, c) laser irradiation or heating in order to obtain d) a single crystalline layer on the host (Si) substrate. Reproduced with permission . Copyright 2006, Wiley‐VCH Verlag GmbH and Co.…”

Silver diffusion bonding and layer transfer of lithium niobate to silicon

“…The combination of these two methods enables thin-film single crystal layer transfer of a wide variety of semiconductors 3-5 and ferroelectrics. [6][7][8] By combining the flexibility of bottom-up processing with the near-ideal optical and electronic properties of single crystal films, these two techniques have become the standard method for producing silicon-on-insulator. 4,5 In addition, wafer bonding and layer transfer has enabled ultrahigh efficiency, multijunction solar cells to be fabricated by bonding lattice-mismatched semiconductors.…”

“…Previous work with lithium niobate and silicon bonding was done using laser-induced forward transfer techniques. 8 This technique minimized thermal expansion mismatch between the two bonding layers by inducing layer transfer using a carbon dioxide laser rather than traditional thermal cycling. In addition to thermal considerations, extensive work is required to ensure surface planarity, smoothness, and cleanliness of the two surfaces; 9-11 however, such processes are expensive and inefficient.…”