# The Opto-Electronic Functional Devices Based on Three-Dimensional Lead Halide Perovskites
## 4 The Fabrication of the LHP Based Devices  
### Massive Integration of LHP Devices  
It is highly desired that massive fabrication of the integrated LHP-based devices could be realized with low cost. To achieve this goal, an effective lithographic approach that can define desired LHP patterns is urgently needed. In general, there are several key points for the effective lithographic approach. Firstly, it is important to cover the LHP with a layer of resist on which the structures with micrometer or submicrometer resolution can be patterned. Secondly, the LHP film, unprotected by patterned resist mask, should be completely removed. Thirdly, the final residual resist mask should also be removed from the LHP film, while the removal will not introduce considerable pollution or damage to the device. [PERSON] et al. reported a method to develop MAPbI\({}_{3}\) film demonstrating micrometer-resolution patterns, using photolithography followed by SF\({}_{6}\) etching [117]. In this approach, desired pattern was defined in photoresist (OSCoR100 negative photoresist) on top of MAPbI\({}_{3}\) film. SF\({}_{6}\) plasma reactive ion etching (RIE) was subsequently used to facilitate pattern transfer. This micrometer-resolution patterning technique of MAPbI\({}_{3}\) was shown to be effective in reducing signal crosstalk between neighboring photodetector pixels. However, the RIE process only modifies the exposed film chemically (converting the material into PbF\({}_{2}\)) but does not remove the LHP layer completely as desired. Additionally, the resolution is limited to micrometer level due to diffraction limit. [PERSON] et al. explored  
Figure 9: Different types of LHP THz modulators and their performances. (**a**). Lateral schematic illustration of the Si/PEDOT:PSS/LHP THz modulator. (**b**). The THz transmission of the hybrid modulator and (**c**). modulation depth (MD) comparison at 0.33 THz for different structure. Reproduced with permission from [21]; published by Wiley, 2020. (**d**). A metamaterial/LHP THz modulator, with the equivalent circuit model of the unit cell shown on the right. (**e**). THz transmittance with and without laser irradiation; (**f**). the MD of the device. Reprinted from [116]. Copyright 2019, with permission from Elsevier. a different fabrication process for LHP devices [118]. In this approach, micro- or nanosized structures were patterned in poly (methyl methacrylate) (PMMA) resist with electron beam lithography (EBL). Inductively coupled plasma (ICP) etching was used to transfer the structures to MAPbBr\({}_{3}\) film. Compared with the conventional LHP photodetector, the advantage of EBL-fabricated photodetector was clearly shown by authors. Even though this method can potentially generate high-resolution features (-nanosize), it is based on EBL process and is thus limited in terms of cost and speed. In addition, the undesired LHP layer could not be removed completely by ICP process. A different approach of pattern transfer, utilizing lift-off instead of etching, was reported by [PERSON] et al. The substrate (polyimide/SiN\({}_{x}\)/Al\({}_{2}\)O\({}_{3}\) and polyimide/SiN\({}_{x}\)/Al\({}_{2}\)O\({}_{3}\)/Au) was initially covered by a double-layer of PMMA resist with different molecular weights in this approach [119]. Subsequently, the resist layer was exposed by deep ultraviolet (DUV) lithography. Then MAPbI\({}_{3}\) film was deposited directly on the substrate by thermal coeaporation where CH\({}_{3}\)NH\({}_{3}\)I (MAI) and PbI\({}_{2}\) were in use as target materials. Finally, the PMMA was dissolved in chlorobenzene, thereby lifting off the undesired MAPbI\({}_{3}\). The PMMA lift-off procedure developed the first demonstration of MAPbI\({}_{3}\) as a gate dielectric revealing extraordinary channel control due to its giant dielectric constant. However, this technique that can realize complete removal of undesired layer requires the evaporation of LHP film, which is not compatible with the spin-coating film preparation method used by above methods.