RU2470409C1 - Method of making niobium oxide-based diode - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to microelectronics. The method of making a niobium oxide-based diode involves forming a lower conducting electrode, a rectifying electrical junction and an upper conducting electrode. The rectifying electrical junction used is a 40-100 nm thick niobium oxide layer with an upper electrode which enables to form a Schottky barrier. The niobium oxide layer is obtained by oxidising the lower electrode which consists of niobium metal. The upper conducting electrode used is metals with a work function higher than 5.1 eV: Ni, Au, Pt, Pd.

EFFECT: invention reduces back current density and increases the ratio of direct to back current by up to seven orders and also enables to use simpler and cheaper low-temperature technology of producing oxide layers, which reduces the cost of making oxide-based diodes.

2 cl, 2 dwg

Description

Application area

The invention relates to the field of microelectronics and can be used as diodes in circuits based on oxide materials prepared by low-temperature methods.

State of the art

Currently, in the field of microelectronics there are a number of problems, the solution of which is not possible on the basis of standard silicon technology (CMOS, etc.). One of the most pressing problems is the need to create a large number of active electronic components on low-temperature substrates of a large area (glass, polymer). Such tasks arise, for example, when creating solar panels or large-area displays. This problem cannot be solved using standard high-temperature silicon technologies. A similar problem also arises with the desire to further increase the degree of integration of microcircuits. By setting the physical size of the chip, the necessary increase in the number of components requires a transition from 2D to 3D integration, which is impossible in the framework of standard high-temperature silicon technology - the creation of the upper layers of elements will destroy the underlying components. This is especially noticeable when developing memory chips. The required amount of memory (more than 1TB) can be implemented on the basis of a multi-storey (stackable) design. The creation of such microcircuits requires the use of low-temperature methods of deposition of materials and the development of fundamentally new effective electronic components based on these materials.

One of the main components of electronic technology are transitions (heterostructures) between materials with different electronic properties. These can be contacts with linear current-voltage characteristics - ohmic contacts, or demonstrating rectification - p-n junctions, Schottky diodes, etc.

The behavior of interfaces between traditional semiconductors (Si, Ge, AIIIBV) is well described by existing models of homo- and heterojunctions between different semiconductors, Schottky barriers, and ohmic contacts. However, to solve the above problems - the creation of effective components using low-temperature methods - it is necessary to attract new materials, primarily metal oxides and semiconductors.

The diodes used in the microelectronic industry in low-voltage circuits related to logic circuits have the following requirements:

1) low reverse current density,

2) a large ratio of forward and reverse current,

3) stable performance up to 5 V.

Currently, the main method for producing diodes includes the following steps:

- the formation of the lower conductive electrodes,

- the formation of a semiconductor layer having p - or n-type conductivity,

- local doping to change the type of conductivity to the opposite with the formation of a p-n junction,

- application of the upper conductive electrodes.

A number of patents are known: US 7875871, US 7902537, US 7829875 [1-3], etc., which describe methods for creating resistive memory elements together with diodes used to eliminate signal interference during selective access. In the presented patents, diodes consist, as a rule, of traditional semiconductors (Si, Ge, AIIIBV). The disadvantage of such diodes is the use of high-temperature CMOS technology, which prevents the transition to 3D integration and the use of flexible electronics in circuits.

Known patent US 6444504 [4], which shows a method for the production of multilayer polycrystalline diodes consisting of an oxide polycrystalline zinc film of ZnO n-type and a layer of Bi ₂ O ₃ p-type. Also, together with ZnO, which is annealed at temperatures above 600 ° C, various complex oxides are used, consisting of compounds Bi ₂ O ₃ , Mn ₃ O ₄ , Co ₃ O ₄ , Sb ₂ O ₃ , Fe ₂ O ₃ and Nb ₂ O ₅ , by homogenization at temperatures of ~ 650 ° C. The disadvantages of this kind of structures are also the high temperature of receipt.

Also known is the patent application US 2009/0045429 A1 [5], which presents a method for producing a device including a diode and a resistive memory cell (1D-1R) random access using thin-film layers of oxides and metals obtained by low-temperature deposition methods.

The oxide diode includes: a lower electrode, a rectifying electrical transition, which is a pn heterojunction between a p-type copper oxide layer and an n-type oxide InZn layer, as well as an upper electrode formed on the InZn oxide layer. The resistive memory element is a layer with a variable resistance, consisting of transition metal oxide (OPM) or metal oxide of perovskite-like structure (SrTiO ₃ , (Pr, Ca) MnO ₃ , BaTiO ₃ , PbTiO ₃ ).

A method of producing an oxide diode according to patent application US 2009/0045429 A1 includes the following.

1. On the substrate or dielectric layer, a lower electrode layer consisting of conductive materials such as metal or metal oxide is applied by vacuum deposition methods. For example, the lower electrode may be formed of Al, Hf, Zr, Zn, W, Co, Au, Pt, Ru, Ir, Ti or a conductive metal oxide.

2. A p-type copper oxide layer is applied to the lower electrode. For example, p-type CuO. The oxide layers of the diode in accordance with an embodiment of the present invention can be formed by physical vapor deposition (PVD), molecular layering (ALD), or chemical vapor deposition (CVD).

3. On the p-type copper oxide layer, an InZn layer of n-type oxide of conductivity, for example InZnO or In ₂ Zn ₂ O _5, is applied. The oxide layer can be formed by methods similar to those for the copper oxide layer.

4. An upper electrode is deposited on the InZn oxide layer, which, like the lower electrode, consists of conductive materials such as metal or metal oxide.

The disadvantages of this oxide structure of the memory are the presence of a relatively high density of the reverse current (~ 10 ^-2 A / cm ² at a voltage of 2 V) and, accordingly, a small ratio of the forward and reverse current (not more than 4 orders of magnitude), which is one of the main parameters of the oxide diode . In addition, the method of producing an oxide diode involves the use of complex and expensive methods for the low-temperature production of oxide layers.

The technical result of the invention is to reduce the density of the reverse current and increase the ratio of forward and reverse current (up to 7 orders of magnitude), as well as to use a simpler and cheaper low-temperature technology for producing oxide layers (for example, anodic oxidation), which makes it possible to cheapen the manufacture of oxide diodes.

The technical result is ensured by the fact that a niobium oxide layer with a thickness of 40 nm to 100 nm is used as a rectifying electric junction, with an upper electrode providing a Schottky barrier, and a thin layer of niobium oxide is obtained by oxidizing the lower electrode consisting of niobium metal. As the upper conductive electrode, metals with a work function of more than 5.1 eV are used: Ni, Au, Pt, Pd.

A method for producing an oxide diode is to create a lower conductive electrode consisting of a niobium metal layer, to obtain a niobium oxide layer by oxidizing the lower electrode and depositing the upper electrodes providing a Schottky barrier in contact with niobium oxide (see Fig. 1).

A Schottky diode is a semiconductor diode with a small voltage drop when directly connected. Schottky diodes use the metal-semiconductor junction as a Schottky barrier (instead of the pn junction, as in conventional diodes). In this case, the work function of the n-type semiconductor should be less than the work function of the metal, and vice versa for the p-type semiconductor.

A method for producing a niobium oxide diode includes the following.

1. A lower electrode consisting of niobium metal with a thickness of more than 100 nm is applied to the substrate by vacuum deposition methods.

2. Next, the lower electrode, consisting of niobium metal, is oxidized; the oxide thickness in this case varies from 40 to 100 nm. Oxidation of the lower electrode can be carried out by low-temperature methods: for example, electrochemical oxidation in electrolytes based on aqueous solutions of acids H ₃ PO ₄ , H ₂ SO ₄ , HNO ₃ and mixtures based on them.

3. A top electrode consisting of metals with a work function of more than 5.1 eV, in particular Ni, Au, Pt, Pd and alloys based on them, is deposited on a layer of anode niobium oxide.

There are a number of metals whose anodic oxidation is well developed and widely represented in the literature: Al, Ti, V, Mo, Nb, Ta, Zr, etc. [6]. These are, as a rule, dielectric films, in addition to V, Nb, and Ti oxides, which possess n-type semiconductor properties. Vanadium (V) is not suitable for creating a Schottky diode, since its oxides have a work function (6.7 eV) [7], greater than the work function of most known metals. Titanium oxide has rather difficult conditions for anodic oxidation - the electrolyte is a molten salt at a temperature of more than 300 ° C, and is not a low-temperature production method.

Compared to a number of limiting oxides Al, Mo, Ta, Zr, etc., obtained by the anodic oxidation method, niobium oxide has less resistance and has a work function of 5.1 eV [8], which makes it possible to create a Schottky diode based on it with a number of metals with high work function, such as Ni (5.04-5.32 eV), Au (5.1-5.47 eV), Pt (5.12-5.93 eV), Pd (5.22-5.6 eV) [9]. It should be noted that with magnetron sputtering of films of a thickness of the order of ~ 100 nm, the metal consumption is small, and the use of relatively expensive metals is much cheaper than obtaining, for example, complex IZO oxide. Anodic oxidation of niobium can be carried out in the galvanostatic and voltstatic modes in electrolytes based on aqueous solutions of acids H ₃ PO ₄ , H ₂ SO ₄ , HNO ₃ and mixtures based on them.

When oxidizing the lower electrode, consisting of niobium metal, it should be borne in mind that the film thickness should be from 40 nm to 100 nm. At a thickness of less than 40 nm, the low breakdown voltage of the film does not ensure stable operation of the diode in the voltage range up to 5V. With a film thickness of more than 100 nm, the resistance of the oxide film begins to make a significant contribution to the resistance of the oxide diode, significantly reducing the direct current density.

List of figures

Figure 1 shows the structure of a Schottky oxide diode. 1 - lower conductive electrode (Nb), 2 - layer of niobium oxide (Nb ₂ O ₅ ), 3 - upper conductive electrode (Ni, Au, Pt, Pd), 4 - electrodes of the external circuit.

Figure 2 shows the current-voltage characteristic of the structure of Nb / Nb ₂ O ₅ / Pd.

The implementation of the invention

Using a DC magnetron sputtering method, a niobium metal layer ~ 100-200 nm thick is deposited on a dielectric substrate. Next, anodic oxidation of the sample is carried out in the electrolyte of a 0.1N aqueous solution of H ₃ PO ₄ in the galvanostatic mode at a current density of 2 mA / cm ² up to a voltage of 12 V. In the next step, DC magnetron sputtering of palladium (Pd) is performed as the upper electrode using lithography methods . Technical characteristics of the Schottky oxide diode are as follows (Fig. 2): current density (at 4 V) direct 10 ² A / cm ² , reverse 10 ^-5 A / cm ² . The ratio of currents, respectively, 10 ⁷ .

Claims (2)

1. A method of producing a niobium oxide diode, including the creation of a lower conductive electrode, a rectifying electric transition and an upper conductive electrode, characterized in that a niobium oxide layer with a thickness of 40 nm to 100 nm with an upper electrode is used as a rectifying electric transition Schottky barrier and a layer of niobium oxide is obtained by oxidation of the lower electrode, consisting of niobium metal. 2. The method of producing a niobium oxide diode according to claim 1, characterized in that metals with an output work of more than 5.1 eV are used as the upper conductive electrode: Ni, Au, Pt, Pd.

Images