Texture Transfer in Dielectric Layers via Nanocrystalline Networks: Insights from in Situ 4D-STEM.

Transition metal oxide dielectric layers have emerged as promising candidates for various relevant applications, such as supercapacitors or memory applications. However, the performance and reliability of these devices can critically depend on their microstructure, which can be strongly influenced by thermal processing and substrate-induced strain. To gain a more in-depth understanding of the microstructural changes, we conducted in situ transmission electron microscopy (TEM) studies of amorphous HfO2 dielectric layers grown on highly textured (111) substrates. Our results indicate that the minimum required phase transition temperature is 180 °C and that the developed crystallinity is affected by texture transfer. Using in situ TEM and 4D-STEM can provide valuable insights into the fundamental mechanisms underlying the microstructural evolution of dielectric layers and could pave the way for the development of more reliable and efficient devices for future applications.

A Sensitivity-Optimized Flexible Capacitive Pressure Sensor with Cylindrical Ladder Microstructural Dielectric Layers.

Flexible capacitive pressure sensors have attracted extensive attention due to their dynamic response and good sensing capability for static and small pressures. Using microstructural dielectric layers is an effective method for improving performance. However, the current state of microstructure design is primarily focused on basic shapes and is largely limited by simulation results; there is still a great deal of potential for further innovation and improvement. This paper innovatively proposes to increase the ladder structure based on the basic microstructures, for example, the long micro-ridge ladder, the cuboid ladder, and cylindrical ladder microstructures. By comparing 9 kinds of microstructures including ladder structure through finite element simulation, it is found that the sensor with a cylindrical ladder microstructure dielectric layer has the highest sensitivity. The dielectric layers with various microstructures are obtained by 3D printed molds, and the sensor with cylindrical ladder microstructure dielectric layer has the sensitivity of 0.12 kPa-1, which is about 3.9 times higher than that without microstructure. The flexible pressure sensor developed by us boasts sensitivity-optimized and operational stability, making it an ideal solution for monitoring rainfall frequency in real time.

Modeling of Self-Aligned Selector Based on Ultra-Thin Metal Oxide for Resistive Random-Access Memory (RRAM) Crossbar Arrays.

Resistive random-access memory (RRAM) is a crucial element for next-generation large-scale memory arrays, analogue neuromorphic computing and energy-efficient System-on-Chip applications. For these applications, RRAM elements are arranged into Crossbar arrays, where rectifying selector devices are required for correct read operation of the memory cells. One of the key advantages of RRAM is its high scalability due to the filamentary mechanism of resistive switching, as the cell conductivity is not dependent on the cell area. Thus, a selector device becomes a limiting factor in Crossbar arrays in terms of scalability, as its area exceeds the minimal possible area of an RRAM cell. We propose a tunnel diode selector, which is self-aligned with an RRAM cell and, thus, occupies the same area. In this study, we address the theoretical and modeling aspects of creating a self-aligned selector with optimal parameters to avoid any deterioration of RRAM cell performance. We investigate the possibilities of using a tunnel diode based on single- and double-layer dielectrics and determine their optimal physical properties to be used in an HfOx-based RRAM Crossbar array.

Controllable Oxidation of ZrS2 to Prepare High-κ, Single-Crystal m-ZrO2 for 2D Electronics.

High-κ materials that exhibit large permittivity and band gaps are needed as gate dielectrics to enhance capacitance and prevent leakage current in downsized technology nodes. Among these, monoclinic ZrO2 (m-ZrO2 ) shows good potential because of its inertness and high-κ with respect to SiO2 , but a method to produce ultrathin single crystal is lacking. Here, the controllable preparation of ultrathin m-ZrO2 single crystals via the in situ thermal oxidation of ZrS2 is achieved. As-grown m-ZrO2 presents an equivalent oxide thickness of ≈0.29 nm, a high dielectric constant of ≈19, and a breakdown voltage (EBD ) of ≈7.22 MV cm-1 . MoS2 field effect transistor (FET) by using m-ZrO2 as a dielectric layer shows comparable mobility to that using SiO2 dielectric. The ultraclean interface of m-ZrO2 /MoS2 and high crystalline quality of m-ZrO2 lead to negligible hysteresis in transfer curves. Single crystal m-ZrO2 dielectric shows potential application in digital complementary metal oxidesemiconductor (CMOS) logic FET.

A Flexible Piezocapacitive Pressure Sensor with Microsphere-Array Electrodes.

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human-machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor's overall performance. However, microstructures usually require complex and costly processes such as photolithography or chemical etching for fabrication. This paper proposes a novel approach that combines self-assembled technology to prepare a high-performance flexible capacitive pressure sensor with a microsphere-array gold electrode and a nanofiber nonwoven dielectric material. When subjected to pressure, the microsphere structures of the gold electrode deform via compressing the medium layer, leading to a significant increase in the relative area between the electrodes and a corresponding change in the thickness of the medium layer, as simulated in COMSOL simulations and experiments, which presents high sensitivity (1.807 kPa-1). The developed sensor demonstrates excellent performance in detecting signals such as slight object deformations and human finger bending.

Surface Polarization Doping in Diketopyrrolopyrrole-Based Conjugated Copolymers Using Cross-Linkable Terpolymer Dielectric Layers Containing Fluorinated Functional Units.

It is essential to tune the electrical properties of inorganic semiconductors via a doping process in the fabrication of cutting-edge electronic devices; however, the doping in organic field-effect transistors (OFETs) is limited by the uncontrollable dopant diffusion and low doping efficiencies. This study proposes the use of a fluorinated functional group in a polymer dielectric layer as an effective p-type doping strategy for ambipolar diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A)-type semiconducting copolymer films used in OFETs, without generating structural perturbations. To experimentally verify the surface polarization doping effect of the fluorinated group, two terpolymers─poly(pentafluorostyrene-co-3-azidopropyl-methacrylate-co-propargyl-methacrylate) (5F-SAPMA), wherein fluorinated units are included, and poly(phenyl-methacrylate-co-3-azidopropyl-methacrylate-co-propargyl-methacrylate) (PhAPMA), without fluorinated units─are designed and synthesized for use in OFETs. The synthesized 5F-SAPMA and PhAPMA films were cross-linked through the click reaction between the alkyne and azide units in the terpolymers at 150 °C to provide chemical, thermal, and mechanical stabilities and solvent resistance. The electrical characterization of the OFETs with the newly synthesized terpolymer dielectrics reveals that the surface polarization induced by the fluorinated groups of the 5F-SAPMA dielectrics leads to the generation of additional hole charges and helps minimize the broadening of the extended tail states in the vicinity of the valence band (highest occupied molecular orbital (HOMO) level). This not only enables a transition from the ambipolar to p-type dominant characteristics but also helps increase the hole mobility from 0.023 to 0.305 cm2/(V·s).

Near-Infrared Organic Phototransistors with Polymeric Channel/Dielectric/Sensing Triple Layers.

A new type of near-infrared (NIR)-sensing organic phototransistor (OPTR) was designed and fabricated by employing a channel/dielectric/sensing (CDS) triple layer structure. The CDS structures were prepared by inserting poly(methyl methacrylate) (PMMA) dielectric layers (DLs) between poly(3-hexylthiophene) (P3HT) channel layers and poly[{2,5-bis-(2-octyldodecyl)-3,6-bis-(thien-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-diyl}-co-{2,2'-(2,1,3-benzothiadiazole)-5,5'-diyl}] (PODTPPD-BT) top sensing layers. Two different thicknesses of PMMA DLs (20 nm and 50 nm) were applied to understand the effect of DL thickness on the sensing performance of devices. Results showed that the NIR-OPTRs with the CDS structures were operated in a typical n-channel mode with a hole mobility of ca. 0.7~3.2 × 10-4 cm2/Vs in the dark and delivered gradually increased photocurrents upon illumination with an NIR light (905 nm). As the NIR light intensity increased, the threshold voltage was noticeably shifted, and the resulting transfer curves showed a saturation tendency in terms of curve shape. The operation of the NIR-OPTRs with the CDS structures was explained by the sensing mechanism that the excitons generated in the PODTPPD-BT top sensing layers could induce charges (holes) in the P3HT channel layers via the PMMA DLs. The optically modulated and reflected NIR light could be successfully detected by the present NIR-OPTRs with the CDS structures.

Structure-Related Optical Characteristics of Thin Metallic Films in the Visible and Ultraviolet.

Surface irregularities and crystalline order strongly influence both the scattered light and absorption of metallic films. These effects extend through all spectral regions but are particularly important in the visible and ultraviolet. Scattered light arises from several scattering mechanisms. Macroscopic irregularities such as dust, scratches and particulates are typically much less important than are microirregularities only a few tens of angstroms in height but covering the entire surface. For metals such as silver and aluminum, which have plasma edges in the ultraviolet, the excitation of surface plasmons resulting from these microirregularities causes additional incoherently reemitted or "scattered" light. Surface plasmon excitation also causes increased absorption in some wavelength regions. These effects are enhanced by dielectric overcoating layers, which both increase the absorption and scattering and shift the wavelength at which the peak occurs. Surface plasmon excitation is particularly important in the ultraviolet region, where the dielectric overcoating applied to prevent formation of an oxide film on aluminized mirrors, for example, can significantly change the mirror reflectance. Plasmon excitation is made possible by a momentum conserving process associated with material inhomogeneities and hence can presumably be caused by crystalline disorder in the metal surface as well as surface irregularities. If the disorder is present on a sufficiently fine scale, it also affects the band structure of the metal and hence its optical absorption. Examples of the effect of film structure on the optical properties of evaporated and sputtered metal films will be given.