Electrical Properties of HfO₂Thin Insulating Film Prepared by Anodic Oxidation

Abstract

Polycrystalline HfO 2 thin film capacitors were prepared by anodizing sputter-deposited Hf films, and their capacitor and leakage current properties were studied. Electrical measurements were performed for the parallel-plate Hf anodized capacitors with an Al-HfO 2 -Hf (metal-insulator-metal) structure, and high capacitance density (0.6 "F/cm 2 ) and low dielectric loss (0.0095) were obtained for a very thin-oxide capacitor anodized at 10 V. In addition, the leakage current density of this capacitor was about 5 Â 10 À9 A/cm 2 at an applied voltage of 5 V. The leakage current density (J) of HfO 2 capacitors as a function of applied electric field (E) was investigated for several capacitors with different oxide thicknesses, by plotting lnðJÞ vs E 1=2 curves. As a result, it was revealed that the conduction mechanism is due to Schottky emission, irrespective of the oxide thickness.

High-temperature conduction behaviors of HfO2/TaN-based metal-insulator-metal capacitors

“…In fact, both static and dynamic dielectric constants have been widely used to deduce the conduction mechanisms of high-dielectric MIM capacitors; 12,16,19,24,25 however, which dielectric constant is applicable depends on the velocity of carriers in the dielectric. In fact, both static and dynamic dielectric constants have been widely used to deduce the conduction mechanisms of high-dielectric MIM capacitors; 12,16,19,24,25 however, which dielectric constant is applicable depends on the velocity of carriers in the dielectric.…”

Direct writing of anodic oxides for plastic electronics

“…e Comparison of capacitance per area and leakage current density with literature. 51,[58][59][60][61][62][63][64][65][66][67][68] Our multilayer capacitors (red symbols) reach record-high capacitance of 4.2 µF cm −2 at sub-10 nA cm −2 leakage current levels oxide and gold electrodes by doping of the oxide, or by fabricating PN-junctions. The semiconducting properties of oxides can be changed with the anodisation process itself, as previously shown for Indium-Tin-oxide.…”

“…3e) for recent reports of dielectric materials and capacitors. 51,[58][59][60][61][62][63][64][65][66][67][68] Here, high-performing capacitors require both a high capacitance per area and a low-leakage current density. Although some materials (like pV3D) show superior leakage behavior compared to anodic Al 2 O 3 , this is typically only achievable by sacrificing the high capacitance per area.…”

Solution-Processed HfOx for Half-Volt Operation of InGaZnO Thin-Film Transistors

“…However, conventional solution-processing methods, such as spin-coating, normally require a high-temperature treatment to effectively reduce the number of defects by curing the film and removing any organic residuals from the surface, making them not suitable for flexible electronic devices. , These defects, such as hydroxyl groups or oxygen vacancies, may act as dielectric/channel interface traps, increasing the subthreshold swing and negatively affecting the mobility and current on/off ratio. , Also, it is still challenging for methods such as spin-coating to achieve an ultrathin dielectric film while maintaining a high uniformity. Anodization has been demonstrated as an alternative solution-based approach for formation of oxide films at room temperature, offering the additional advantages of being pinhole-free, conformal to the underlying metal, and capable of forming thin films with a high level of uniformity over large areas. − The anodized material’s properties depend on the electrolyte, voltage, and current density used, and the thickness of the anodized film is found to be proportional to the applied potential. , Although anodization has been studied for use in electrical, electronic, and optoelectronic devices and systems for decades, − the study on using anodized high-κ materials as gate dielectric, especially for low-voltage oxide TFTs, has only been started recently. − For example, IGZO TFTs were recently demonstrated to operate within 1 V using anodized Al x O y as gate dielectrics. , However, the relatively low dielectric constant of Al 2 O 3 limits the capacitance density that is achievable and therefore prevents further reduction of the operating voltage without sacrificing the device mobility, current on/off ratio, and so on. , An alternative approach is to use HfO 2 , which has a higher κ (20–25) and suitable energy band offsets . Therefore, HfO 2 can have a greater thickness than Al 2 O 3 while still giving the same capacitance density, which suppresses the leakage current significantly.…”

“…Hence, it is of interest to optimize the anodization voltage for achieving low-voltage, high-performance TFTs. Also, with the decrease of anodization voltage, a thin dielectric film results and such a film might possess chemical and physical properties that differ significantly from thicker films. , However, until now, the few studies of anodized HfO x in the literature have all focused on high anodization voltages (≥5 V) and relatively thick films (>20 nm). ,, Hence, it is worth exploring the properties of ultrathin HfO x films that were achieved by further decreasing the anodization voltages and the electrical performance of the resulting TFTs. A further advantage of ultrathin films is their excellent mechanical flexibility, which opens up potential application as low-voltage, low-power wearable electronics .…”