Mechanism Of Hetero Integration And Domain Regulation Of LiNbO₃ Ferroelectric Single Crystal Films

Lithium niobate(LN)is a kind of multifunctional crystal with extensive application prospect,which has excellent ferroelectric,nonlinear,photorefractive,piezoelectric,electrooptic and acousto-optic properties.In recent years,with the rapid development of intelligent terminals and high-speed communication,traditional domain engineering is difficult to solve the problems of large lateral dimension,high power consumption,low performance of devices and so on.By greatly reducing the polarization electric field,the LN film on insulator(LNOI)can achieve miniaturization,high integration and low power consumption of domain engineering devices,which leads to the breakthrough of traditional LN device performance bottlenecks.Therefore,it is of great scientific significance for the functional upgrading and application promotion of LN domain engineering to study the mechanism of heterogeneous integration and domain regulation of LN thin films.In this thesis,three aspects of LN film process optimization,micro-domain thermal stability and domain wall conduction enhancement are studied,and thermally induced metastable domains and domain wall current are tested and analyzed.Firstly,the lowtemperature direct bonding and ICP dry etching process optimization are optimized.The plasma activation technology is used to solve the thermal stress mismatch problem on the bonding surface,and then the relationship between temperature,pressure and bonding quality is verified;The ICP dry etching technique is used to improve the etching accuracy of LN,and then the etching of LN in photoresist and metal mask is analyzed.Secondly,by analyzing the dynamic model of domain polarization reversal caused by electric field at room temperature,the growth mechanism of metastable domain is revealed.The theoretical model of thermally induced metastable domain evolution is established,based on which a method for enhancing the thermal stability of the domain inversion is proposed.Finally,the mechanism of domain wall inclination affecting domain wall conduction is analyzed qualitatively,and the mechanism of small amplitude DC bias voltage enhancing domain wall current is revealed,so as to realize stable domain wall conduction.In the process optimization of LN thin film,a low temperature direct bonding scheme at 150 ? and 10000 N pressure is proposed by using semiconductor heterogeneous integration platform.And accurate etching of 8×8 ?m boss structure with a depth of 400 nm is achieved through ICP dry etching technology.In the aspect of LN thin film electric domain control,the polarization of 300 nm wide thin film electric domain is realized by voltage power microscope,the structural evolution of metastable electric domain during heating-cooling process was recorded,and thermal stability of reversed electric domain increased from 55~85 °C to more than 150 °C.In the aspect of domain wall current regulation,a small amplitude DC bias voltage is applied by a conductive force microscope to modulate the domain wall inclination.As a result,the domain wall current increases from 30 pA to 100 pA.