•The thin-film-transistors (TFTs) with atomic-layer-deposited Al-doped ZnO channels have been fabricated under the maximum process temperature of 200 °C.•Different from the polycrystalline ZnO film, the Al-doped ZnO film can maintain an amorphous matrix by increasing Al concentration.•The adoption of Al-doped ZnO channel improves significantly the stability of the device under illumination and gate bias stress.•The Al-doped ZnO channel demonstrates stronger immunity to the surrounding ambient than the ZnO channel.The electrical characteristics of TFTs with atomic-layer-deposited ZnO:Al (ZAO) channels have been studied in this work. By increasing Al doping concentration, the ZAO film changes from polycrystalline to amorphous, and its bandgap widens as well. With post-annealing at 200 °C, the superior electrical stabilities under illumination and gate bias stress were achieved in ZAO TFTs compared with ZnO TFTs. For the strong immunity to illumination in ZAO TFTs, it is attributed to the widening bandgap of channel material for the reduction of the carrier concentration. While for the improved electrical stability under positive bias stress, it is mainly due to the suppression of interactions between the amorphous channel and the surrounding ambient, which is verified by the observations in N2 ambient.

Organic semiconducting/ferroelectric blend films attracted much attention due to their electrical bistability and rectification properties and thereof the potential in resistive memory devices. During film deposition from the blend solution, spinodal decomposition induced phase separation, resulting in discrete semiconducting phase whose electrical property could be modulated by the continuous ferroelectric phase. However, blend films processed by common spin coating method showed extremely rough surfaces, even comparable to the film thickness, which caused large electrical leakage and thus compromised the resistive switching performance. To improve film roughness and thus increase the productivity of these resistive devices, we developed temperature controlled spin coating technique to carefully adjust the phase separation process. Here we reported our experimental results from the blend films of ferroelectric poly(vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) and semiconducting poly(3-hexylthiophene) (P3HT). We conducted a series of experiments at various deposition temperatures ranging from 20 to 90 °C. The resulting films were characterized by AFM, SEM, and VPFM to determine their structure and roughness. Film roughness first decreased and then increased with the increase of deposition temperature. Electrical performance was also characterized and obviously improved insulating property was obtained from the films deposited between 50 and 70 °C. By temperature control during film deposition, it is convenient to efficiently fabricate ferroelectric/semiconducting blend films with good electrical bistability.Keywords: ferroelectric/semiconducting blend films; phase separation; resistive switching; spin coating

Mesoporous organosilica (MO) films are prepared using precursor 1,2-bis(triethoxysilyl)ethane (BTEE) and porogen template poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (P123). The effects of annealing temperature, P123/BTEE molar ratio, and moisture adsorption on the characteristics of the MO films are investigated. It is indicated that MO films prepared at a P123/BTEE molar ratio of 0.016 display the lowest dielectric constant (κ) of 1.80, a small dissipation factor of 0.0068 at 100 kHz, an extremely low leakage current density of 2.01 × 10−9 A cm−2 at 0.5 MV cm−1, a modulus (E) of 6.27 GPa, and a hardness (H) of 0.58 GPa. Following moisture adsorption, the κ value increases by ∼12%. However, ultraviolet treatment significantly reduces the extent of increase of the κ value to 4%. The films maintain an ultralow κ value of ∼2.0 and a very low leakage current density of 1.7 × 10−9 A cm−2 at 0.5 MV cm−1. Following annealing at 500 °C, the superior performance of the MO films is demonstrated by their κ value of ∼1.92, leakage current density of 7.08 × 10−9 at 0.5 MV cm−1, and improved E of ∼9.1 GPa and H of ∼0.8 GPa. Such MO films are very promising for advanced interlevel insulators.

Ferroelectric polymers are a kind of promising materials for low-cost flexible memories. However, the relatively high thermal annealing temperature restricts the selection of some flexible polymer substrates. Here we report an alternative method to obtain ferroelectric poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films under low process temperatures. Spin-coated P(VDF-TrFE) thin films were solvent vapor processed at 30 °C for varied times. Structural analyses indicated that solvent vapor annealing induced crystallization to form a ferroelectric β phase, and electrical measurements from both macroscopic ferroelectric switching and microscopic vertical piezoresponse force microscopy further proved the films enduring solvent vapor annealing for suitable short times possessed good ferroelectric and piezoelectric properties. To illuminate the application of solvent vapor annealing on ferroelectric devices, we further fabricated ferroelectric capacitor memory devices with a structure of Al/P(VDF-TrFE)/Al2O3/p-Si/Al where the ferroelectric layer was solvent vapor annealed. Ferroelectric capacitors showed obvious bistable operation and comparable ON/OFF ratio and retention performance. Our work makes it possible to structure ferroelectric devices on flexible substrates that require low process temperatures.Keywords: ferroelectric polymer; P(VDF-TrFE); solvent vapor annealing

•SiO2/TiO2/SiO2 (STS) dielectrics were formed by atomic-layer-deposition for MIM capacitor.•Compared with TiO2, the STS dielectrics can improve significantly the leakage characteristics.•The conduction mechanisms of the STS MIM capacitor were discussed.A new concept of SiO2/TiO2/SiO2 (STS) sandwiched dielectrics has been successfully prepared by atomic-layer-deposition technique for high density MIM capacitor applications. Compared with pure TiO2 dielectric, the addition of ultra-thin (2 nm) SiO2 layers reduces significantly the leakage current and enhances the breakdown electric field of MIM capacitor. Accordingly, the STS MIM capacitor exhibits a high capacitance density of around 12.4 fF/μm2 at 100 kHz, and a leakage current density of 8.8 × 10−7 A/cm2 at −1 V, which is about three orders of magnitude smaller than that of the pure TiO2 MIM capacitor. Furthermore, the conduction mechanisms of the STS capacitor have been investigated, revealing that the Poole–Frenkel emission is dominated in the high field range, and the extracted energy barrier separating the traps from the conduction band is in a 0.85–0.90 eV range.Graphical abstract

The different charge trapping materials HfO2, HfAlO and Al2O3 have been compared electrically in metal-oxide-semiconductor capacitors with fixed Al2O3 tunneling and blocking layers and Pd-electrode. The capacitance–voltage hysteresis window, memory window, and stress-time dependent flat-band voltage shift increase with increasing the relative content of HfO2 in the charge trapping layer under the same measurement conditions. After programming at + 17 V for 0.1 s and erasing at − 17 V for 0.1 s, successively, the resulting memory window increases from 0.4 V to 3.8 V with increasing the content of HfO2 from 0% (Al2O3) to 100% (HfO2). However, the charge retention of the capacitors gradually worsens in the sequence of Al2O3, HfAlO and HfO2, which accords with the leakage characteristics of the capacitors. Our results reveal that HfAlO (A:H = 1:1) is a more promising charge trapping material than HfO2 and Al2O3 for polysilicon–oxide–nitride–oxide–silicon type memory applications. This is attributed to enough charge storage capacity, high thermal stability and medium dielectric constant.Highlights► Al2O3, HfAlO and HfO2 are compared as charge trapping layer of memory device. ► The memory window increases with the HfO2 content in the layers. ► The charge retention worsens in the sequence Al2O3, HfAlO and HfO2. ► The underlying mechanisms are discussed.

Two novel 3′,4′,5′-trifluorobiphenyl-based aromatic polyimide monomers, 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′-biphenyl diamine (BTFBPD) and 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BTFBPDA) were synthesized. Two fluorinated polyimides (PIs), PI(BTFBPD-DPBPDA) and PI(BTFBPD-BTFBPDA) were prepared via a two-step procedure using BTFBPD reacting with 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DPBPDA) and BTFBPDA, respectively. BTFBPD was characterized with single crystal X-ray diffraction analysis and the geometric parameters showed the noncoplanar twisted character. PIs exhibited highly organo-solubility and thermal stability. The PI films sandwiched between an indium-tin oxide(ITO) bottom electrode and Al top electrode exhibited two accessible conductivity states and can be switched from the low-conductivity to the high-conductivity. The memory devices with the configuration of Al/PI(BTFBPD-DPBPDA)/ITO exhibited a flash type memory capability, whereas the Al/PI(BTFBPD-BTFBPDA)/ITO presented a write once read many times (WORM) memory capability. The fabricated devices showed low turn-on threshold voltages of −1.3 V (PI(BTFBPD-DPBPDA)) and −1.7 V (PI(BTFBPD-BTFBPDA)) and both ON/OFF current ratios on the order of 103 to 104.

Two novel polyimides, PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA), consisting of alternating electron-donating 2,2′-bis[4-(9H-carbazol-9-yl)phenyl]- or 2,2′-bis[4-(diphenylamino)phenyl]-substituted biphenyl moieties and electron-accepting phthalimide moieties were synthesized and characterized. These polyimides are thermally stable with 5% weight loss over 500 °C and the glass transition temperatures of the polyimides were found to be 293 °C. The optical band gaps of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were 3.42 and 3.30 eV, respectively, indicating the significance of the linkage groups. The estimated energy levels (HOMO, LUMO) of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were (−5.51, −2.10) and (−5.22, −2.02) eV, respectively. Resistive switching devices with the configuration of Al/polymer/ITO were constructed from these polyimides by using the conventional solution coating process. The as-fabricated PI(CzBD-BTFBPDA) film exhibited a nonvolatile bipolar write-once–read-many times (WORM) memory character, whereas devices with the PI(TPABD-BTFBPDA) film showed “write–read–erase” flash type memory capability. The ON/OFF current ratios of the devices were both around 106 in the ambient atmosphere. The mechanisms associated with the memory effect were further elucidated from the density functional theory (DFT) method at the B3LYP level with the 6-31G(d) basis set. The present study suggested that the tunable switching behavior could be achieved through the appropriate design of the donor–acceptor PIs structure to have potential applications for memory devices.

Ultralow-dielectric-constant (k) porous SiCOH films have been prepared using 1,2-bis(triethoxysilyl)ethane, triethoxymethylsilane, and a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer template by means of spin-coating. The resulting films were characterized by cross-section scanning electron microscopy, small-angle x-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, nanomechanical testing, and electrical measurements. Thermal treatment at 350°C for 2 h resulted in the formation of ultralow-k films with k of ∼2.0, leakage current density of 3 × 10−8 A/cm2 at 1 MV/cm, reduced modulus (Er) of ∼4.05 GPa, and hardness (H) of ∼0.32 GPa. After annealing between 400°C and 500°C for 30 min, the resulting films showed fluctuant k values of 1.85 to 2.22 and leakage current densities of 3.7 × 10−7 A/cm2 to 3 × 10−8 A/cm2 at 0.8 MV/cm, likely due to the change of the film microstructure. Compared with 350°C annealing, higher-temperature annealing can improve the mechanical strength of the ultralow-k film, i.e., Er ≈ 5 GPa and H ≈ 0.56 GPa after 500°C annealing.

We investigate the influence of pulse-plated Ni barriers, compared to direct current (DC)-plated Ni barriers, on the growth of Sn whiskers in laminated Cu/Ni/Sn samples. The results indicate that the pulse-plated Ni barriers exhibit much better resistance to Sn whisker growth than the DC-plated Ni barriers, i.e., when exposed to ambient of 60°C and 93% relative humidity (RH) for 40 days only a few small hillocks were observed as opposed to the long whiskers and large nodules of Sn for the DC-plated Ni barriers. The underlying mechanisms are addressed based on the texture characteristics of the plated Ni and Sn layers and the formation of intermetallic compounds.

Metal-insulator-silicon capacitors have been fabricated using novel insulators of SiO2/HfO2-Al2O3-HfO2 (HAH)/Al2O3 and metallic HfN gate, exhibiting a program-erasable characteristic. The memory capacitor presents a large memory window of 2.4 V under +12 V program/–14 V erase for 10 ms, no erase saturation, and sufficient electron- and hole-trapping efficiencies such as an electron density of ∼7 × 1012 cm–2 under 13 V program for 0.5 ms and a hole density of ∼4 × 1012 cm–2 under –12 V erase for 0.5 ms. The observed properties are attributed to the introduction of high permittivity atomic-layer-deposited HAH/Al2O3 as well as high work function HfN gate. The related mechanism is addressed accordingly.

Mesoporous organosilica (MO) films are prepared using precursor 1,2-bis(triethoxysilyl)ethane (BTEE) and porogen template poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (P123). The effects of annealing temperature, P123/BTEE molar ratio, and moisture adsorption on the characteristics of the MO films are investigated. It is indicated that MO films prepared at a P123/BTEE molar ratio of 0.016 display the lowest dielectric constant (κ) of 1.80, a small dissipation factor of 0.0068 at 100 kHz, an extremely low leakage current density of 2.01 × 10−9 A cm−2 at 0.5 MV cm−1, a modulus (E) of 6.27 GPa, and a hardness (H) of 0.58 GPa. Following moisture adsorption, the κ value increases by ∼12%. However, ultraviolet treatment significantly reduces the extent of increase of the κ value to 4%. The films maintain an ultralow κ value of ∼2.0 and a very low leakage current density of 1.7 × 10−9 A cm−2 at 0.5 MV cm−1. Following annealing at 500 °C, the superior performance of the MO films is demonstrated by their κ value of ∼1.92, leakage current density of 7.08 × 10−9 at 0.5 MV cm−1, and improved E of ∼9.1 GPa and H of ∼0.8 GPa. Such MO films are very promising for advanced interlevel insulators.

Two novel polyimides, PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA), consisting of alternating electron-donating 2,2′-bis[4-(9H-carbazol-9-yl)phenyl]- or 2,2′-bis[4-(diphenylamino)phenyl]-substituted biphenyl moieties and electron-accepting phthalimide moieties were synthesized and characterized. These polyimides are thermally stable with 5% weight loss over 500 °C and the glass transition temperatures of the polyimides were found to be 293 °C. The optical band gaps of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were 3.42 and 3.30 eV, respectively, indicating the significance of the linkage groups. The estimated energy levels (HOMO, LUMO) of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were (−5.51, −2.10) and (−5.22, −2.02) eV, respectively. Resistive switching devices with the configuration of Al/polymer/ITO were constructed from these polyimides by using the conventional solution coating process. The as-fabricated PI(CzBD-BTFBPDA) film exhibited a nonvolatile bipolar write-once–read-many times (WORM) memory character, whereas devices with the PI(TPABD-BTFBPDA) film showed “write–read–erase” flash type memory capability. The ON/OFF current ratios of the devices were both around 106 in the ambient atmosphere. The mechanisms associated with the memory effect were further elucidated from the density functional theory (DFT) method at the B3LYP level with the 6-31G(d) basis set. The present study suggested that the tunable switching behavior could be achieved through the appropriate design of the donor–acceptor PIs structure to have potential applications for memory devices.

Two novel 3′,4′,5′-trifluorobiphenyl-based aromatic polyimide monomers, 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′-biphenyl diamine (BTFBPD) and 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BTFBPDA) were synthesized. Two fluorinated polyimides (PIs), PI(BTFBPD-DPBPDA) and PI(BTFBPD-BTFBPDA) were prepared via a two-step procedure using BTFBPD reacting with 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DPBPDA) and BTFBPDA, respectively. BTFBPD was characterized with single crystal X-ray diffraction analysis and the geometric parameters showed the noncoplanar twisted character. PIs exhibited highly organo-solubility and thermal stability. The PI films sandwiched between an indium-tin oxide(ITO) bottom electrode and Al top electrode exhibited two accessible conductivity states and can be switched from the low-conductivity to the high-conductivity. The memory devices with the configuration of Al/PI(BTFBPD-DPBPDA)/ITO exhibited a flash type memory capability, whereas the Al/PI(BTFBPD-BTFBPDA)/ITO presented a write once read many times (WORM) memory capability. The fabricated devices showed low turn-on threshold voltages of −1.3 V (PI(BTFBPD-DPBPDA)) and −1.7 V (PI(BTFBPD-BTFBPDA)) and both ON/OFF current ratios on the order of 103 to 104.

Oxygen-free and low resistivity nickel (Ni) thin films are successfully prepared by plasma-assisted atomic layer deposition using nickelocene (NiCp2) as a metal precursor and ammonia (NH3) as a reactant. The properties of the deposited films are characterized by means of X-ray photoelectron spectroscopy, X-ray diffraction, ultraviolet photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy and four-point-probe measurements. The results indicate that the as-deposited films are Ni-dominated materials with small quantities of C and N, containing Ni–Ni, Ni–C, Ni–N, C–N and C–C bonds. Moreover, the films also exhibit excellent conformality on Si nano-pillars with an aspect ratio of ∼13. As the deposition temperature increases from 160 to 280 °C, the film resistivity reduces from ∼127 to ∼71 μΩ cm, which is related to the gradually enhanced Ni3C phase in the films. However, the work function of the film shows a weak dependence on the deposition temperature, increasing from 4.003 to 4.046 eV. After being annealed at 400 °C in the forming gas (N2/4%-H2), the resistivity is reduced significantly down to 11.8 μΩ cm, and the work function increases up to 4.136 eV. These are ascribed to an increase in the purity of the films, as demonstrated by the disappearance of N and the loss of C in the post-annealed films. Such a preparation technique of high quality Ni nano-films is very promising for advanced integrated circuits.