Improved critical-current-density uniformity by using anodization

Abstract

We discuss an anodization technique for a Nb superconductive-electronics-fabrication process that results in an improvement in critical-current-density uniformity across a 150-mm-diameter wafer. We outline the anodization process and describe the metrology techniques used to determine the NbO thickness grown. In the work described, we performed critical current measurements on Josephson junctions distributed across a wafer. We then compared the uniformity of pairs of wafers, fabricated together, differing only in the presence or absence of the anodization step. The cross-wafer standard deviation of was typically 5% for anodized wafers but 15% for unanodized wafers. This difference in uniformity is suggestive of an in-process modification from an unknown cause that is blocked by the anodic oxide. It is interesting that small junctions do not see an improvement in uniformity-apparently the anodization improves only the uniformity and not the variation in junction size. Control of is important for all applications of superconductive electronics including quantum computation and rapid single-flux quantum (RSFQ) circuitry.

Fabrication Process and Properties of Fully-Planarized Deep-Submicron Nb/Al– $\hbox{AlO}_{\rm x}\hbox{/Nb} $ Josephson Junctions for VLSI Circuits

“…After patterning the photoresist mask, the JJ counter electrode was etched using a high-density plasma etcher and then anodized to prevent degradation of the exposed AlO x barrier [27]- [29]. The sizes of the etched JJs were measured before and after the anodization step, and are shown in Fig.…”

Resonant Readout of a Persistent Current Qubit

“…The device was fabricated with a planarized Nb trilayer process at MIT Lincoln Laboratory [9]. The PC qubit is a superconducting loop interrupted by three Josephson junctions.…”

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.…”