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Amorphous SiC with embedded Cu nanoparticles (a-SiC:Cu) was investigated as the insulator layer of Cu/a-SiC:Cu/Au resistive memory. The effect of the Cu embedding on resistive switching characteristics was studied for 20 and 30 vol% Cu. Reduced forming and SET voltages and increased endurance was observed for devices with 30Cu%. At the same time, all key advantageous characteristics of amorphous SiC resistive memory such as ON/OFF ratio of 107 and the co-existence of bipolar and unipolar modes were maintained upon Cu embedding. All above suggests that Cu embedding could be considered as a promising method to improve the overall performance of Cu/a-SiC:Cu/Au resistive memories.

Process details for one growth supercycle in the supercycled ALD process used in this study. Figure S1. Diffraction intensity ratio of the ZnO (0 0 2) peak to (1 0 1) peak as a function of O2 plasma times with fixed thermal cycle (m = 1). Figure S2. (a, d) The fitted refractive index n, (b, e) extinction coefficient k, and (c, f) plot of (αhν)2 as a function of photo energy of ZnO films grown from different O2 plasma times with fixed thermal cycle (m = 1) and different thermal cycles with fixed O2 plasma time (t 3 = 1 s) by the supercycled ALD process. Figure S3. AFM images of the supercycled ALD-grown ZnO films with O2 plasma times of (a) 0 s, (b) 1 s, (c) 2 s, (d) 4 s, and (e) 8 s and fixed thermal cycle (m = 1). Figure S4. Electronic energy levels of the tip sample system for three different cases. (a) Tip and sample are not electrically connected; (b) tip and sample are electrically connected with Fermi energy levels lined up; (c) an external bias equals to the contact potential difference V CPD is applied to the tip. Figure S5. Two-dimensional contact potential difference V CPD images of the surface potential measurements of the supercycled ALD-grown ZnO films with thermal cycles varying from (a) 2, (b) 3, and (c) 5 at fixed O2 plasma time (t 3 = 1 s). Figure S6. XPS spectra and their Gaussian fittings of the O 1s region of the supercycled ALD-grown ZnO films with thermal cycles varying from (a) 2, (b) 3, and (c) 5 at fixed O2 plasma time (t 3 = 1 s). (DOCX 1919 kb)

Supplementary information.

Cu/a-SiC/Au non-volatile resistive memories were fabricated and characterized.Co-existence of bipolar and unipolar resistive switching behavior was reported.Ultrahigh ON/OFF switching ratios in the range of 108-109 were reported.Excellent state retention up to 10years was also demonstrated. Amorphous SiC based resistive memory Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. Co-existence of bipolar and unipolar behavior has been observed with ON/OFF current ratio in the range of 108-109. These high ratios are due to the conduction in the OFF state being dominated by the Schottky barrier between the Au and SiC. ON/OFF ratios exceeding 107 over 10years were predicted from retention characterization. The unique performance combination of the extremely high ON/OFF ratio, coexistence of bipolar and unipolar switching modes as well as excellent stability and retention suggest significant application potentials of Cu/a-SiC/Au RM devices.

Resistive memories (RMs) using amorphous SiC (a-SiC) as the solid electrolyte material have been developed with a Cu/a-SiC/Au stack configuration. Excellent non-volatile bipolar switching characteristics have been observed. An extremely high ON/OFF current ratio in the order of 109 has been observed corresponding to distinctive low (LRS) and high (HRS) resistance states, which is potentially beneficial for future RM applications with reliable state detection and simple periphery circuits. The deposited a-SiC has been extensively characterised for its micro/nanostructures, chemical composition as well as electrical properties. The switching mechanism is investigated through detailed analysis of corresponding I–V curves. The results imply a filamentary conduction mechanism at LRS and Schottky emission mechanism at HRS, especially in the subsequent switching cycles. The contrasting conducting material properties and mechanisms at LRS and HRS contribute to the high ON/OFF ratio. Overall, Cu/a-SiC based RMs demonstrate a number of high performance potentials.

The neutral, distorted octahedral complex [TiCl4(Se n Bu2)2] (1), prepared from the reaction of TiCl4 with the neutral Se n Bu2 in a 1:2 ratio and characterized by IR and multinuclear (1H, 13C{1H}, 77Se{1H}) NMR spectroscopy and microanalysis, serves as an efficient single-source precursor for low-pressure chemical vapor deposition (LPCVD) of titanium diselenide, TiSe2, films onto SiO2 and TiN substrates. X-ray diffraction patterns on the deposited films are consistent with single-phase, hexagonal 1T-TiSe2 (P3m1), with evidence of some preferred orientation of the crystallites in thicker films. The composition and structural morphology was confirmed by scanning electron microscopy (SEM), energy dispersive X-ray, and Raman spectroscopy. SEM imaging shows hexagonal plate crystallites growing perpendicular to the substrate, but these tend to align parallel to the surface when the quantity of reagent is reduced. The resistivity of the crystalline TiSe2 films is 3.36 ± 0.05 × 10-3 Ω·cm with a carrier density of 1 × 1022 cm-3. Very highly selective film growth from the reagent was observed onto photolithographically patterned substrates, with film growth strongly preferred onto the conducting TiN surfaces of SiO2/TiN patterned substrates. TiSe2 is selectively deposited within the smallest 2 μm diameter TiN holes of the patterned TiN/SiO2 substrates. The variation in crystallite size with different diameter holes is determined by microfocus X-ray diffraction and SEM, revealing that the dimensions increase with the hole size, but that the thickness of the crystals stops increasing above ∼20 μm hole size, whereas their lengths/widths continue to increase.

The neutral complexes [GaCl3(EnBu2)] (E = Se or Te), [(GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n = 2; E = Te, n = 3), and [(GaCl3)2{tBuTe(CH2)3TetBu}] are conveniently prepared by reaction of GaCl3 with the neutral EnBu2 in a 1:1 ratio or with nBuE(CH2)nEnBu or tBuTe(CH2)3TetBu in a 2:1 ratio and characterized by IR/Raman and multinuclear (1H, 71Ga, 77Se{1H}, and 125Te{1H}) NMR spectroscopy, respectively, all of which indicate distorted tetrahedral coordination at Ga. The tribromide analog, [GaBr3(SenBu2)], was prepared and characterized similarly. A crystal structure determination on [(GaCl3)2{tBuTe(CH2)3TetBu}] confirms this geometry with each pyramidal GaCl3 fragment coordinated to one Te donor atom of the bridging ditelluroether, Ga–Te = 2.6356(13) and 2.6378(14) A. The nBu-substituted ligand complexes serve as convenient and very useful single source precursors for low pressure chemical vapor deposition (LPCVD) of single phase gallium telluride and gallium selenide, Ga2E3, films onto SiO2 and TiN substrate...

Neutral telluro- and seleno-ether complexes of the form [GaCl3(nBu2E)] (E = Se, Te) and [(GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n = 2; E = Te, n = 3) have been synthesised via a facile, high yielding reaction. These complexes have been shown to be suitable precursors for the low pressure chemical vapour deposition of Ga2Te3 and Ga2Se3, the first reported example of a telluroether complex being used for the deposition of a metal telluride. The thin films have been characterised by X- ray diffraction, SEM, EDX, Raman and Hall measurements. The films are crystalline, have good, uniform coverage and Raman spectra match literature values. Hall measurements show that the thin films are p-type semiconductors. Competitive deposition of Ga2Te3 onto photolithographically patterned SiO2/TiN substrates shows a preference for deposition onto TiN.

Resistive switching of W/amorphous (a)-SiOxCy:H/Cu resistive memories incorporating solely native back-end-of-line (BEOL) materials were studied. A-SiC1.1:H, a-SiO0.9C0.7:H, and a-SiO1.5C0.2:H were exploited as switching layers for resistive memories which all show resistive-switching characteristics with ultrahigh ON/OFF ratios in the range of 106 to 1010. Ohmic conduction in the low resistance state is attributed to the formation of Cu conductive filament inside the a-SiOxCy:H switching layer. Rupture of the conductive filament leads to current conduction dominated by Schottky emission through a-SiOxCy:H Schottky contacts. Comparison of the switching characteristics suggests composition of the a-SiOxCy:H has influences on VFORM and VSET, and current conduction mechanisms. These results demonstrate the capability to achieve functional W/a-SiOxCy:H/Cu using entirely BEOL native materials for future embedded resistive memories.Resistive switching of W/amorphous (a)-SiOxCy:H/Cu resistive memories incorporating solely native back-end-of-line (BEOL) materials were studied. A-SiC1.1:H, a-SiO0.9C0.7:H, and a-SiO1.5C0.2:H were exploited as switching layers for resistive memories which all show resistive-switching characteristics with ultrahigh ON/OFF ratios in the range of 106 to 1010. Ohmic conduction in the low resistance state is attributed to the formation of Cu conductive filament inside the a-SiOxCy:H switching layer. Rupture of the conductive filament leads to current conduction dominated by Schottky emission through a-SiOxCy:H Schottky contacts. Comparison of the switching characteristics suggests composition of the a-SiOxCy:H has influences on VFORM and VSET, and current conduction mechanisms. These results demonstrate the capability to achieve functional W/a-SiOxCy:H/Cu using entirely BEOL native materials for future embedded resistive memories.

Amorphous silicon carbide resistive memory cells are shown to exhibit the highest ROFF/RON ratio recorded for any resistive memory in pulsed switching. The switching characteristics are investigated and fitted to a numerical model. The SET mechanism for these cells is found to be due to ionic motion without joule heating contributions, leading to large VSET. The high thermal conductivity and resistivity of the SiC memory cells result in slow switching but, with high state and thermal stability, show potential for harsh environment use. Radiation properties of SiC memory cells are investigated. No change was seen in switching properties nor in conductive mechanism, up to 2Mrad(Si) using 60Co ionizing gamma radiation.

We report the properties of a series of electrodeposited Ge-Sb-Te alloys with various compositions. It is shown that the Sb/Ge ratio can be varied in a controlled way by changing the electrodeposition potential. This method opens up the prospect of depositing Ge-Sb-Te super-lattice structures by electrodeposition. Material and electrical characteristics of various compositions have been investigated in detail, showing up to three orders of magnitude resistance ratio between the amorphous and crystalline states and endurance up to 1000 cycles.

We report here a ZrO2−x /ZrO2-based bilayer resistive switching memory with unique properties that enables the selection of the switching mode by applying different electroforming current compliances. Two opposite polarity modes, positive bipolar and negative bipolar, correspond to the switching in the ZrO2 and ZrO2−x layer, respectively. The ZrO2 layer is proved to be responsible for the negative bipolar mode which is also observed in a ZrO2 single layer device. The oxygen deficient ZrO2−x layer plays the dominant role in the positive bipolar mode, which is exclusive to the bilayer memory. A systematic investigation of the ZrO2−x composition in the bilayer memory suggests that ZrO1.8 layer demonstrates optimum switching performance with low switching voltage, narrow switching voltage distribution and good cycling endurance. An excess of oxygen vacancies, beyond this composition, leads to a deterioration of switching properties. The formation and dissolution of the oxygen vacancy filament model has been proposed to explain both polarity switching behaviours and the improved properties in the bilayer positive bipolar mode are attributed to the confined oxygen vacancy filament size within the ZrO2−x layer.

TiN/HfOx/TiN resistive RAM (RRAM) devices have been fabricated where the hafnium oxide layer has been deposited at three different temperatures via atomic layer deposition (ALD). Material characterization shows the structure of the hafnium oxide is converted from cubic to monoclinic for 400 degrees C. Elemental analysis shows that the temperature affects the stoichiometric behavior of hafnium oxide, with a higher oxygen concentration at 350 degrees C and above. The switching behavior differs significantly for each device whereby the 400 degrees C device shows no successful switching, due to the change in structure to monoclinic. The two lower temperatures both show successful bipolar switching which set at negative voltages. The 300 degrees C device has a higher Roff/Ron of 13.9, with superior endurance. The 350 degrees C device has a lower Roff/Ron of 5.5 and shows deterioration in switching properties as the number of cycles are increased. At 300 degrees C, the oxygen hafnium ratio is at a minimum; hence the greatest amount of oxygen vacancies are present, which results in improved switching characteristics. This supports the theory that oxygen vacancies play a key role in the switching mechanism for metal oxide RRAM devices.

High quality, nanostructured Bi2Te3,with an unprecedented degree of positional and orientational control of the material form on the nanoscale, is readily obtained by low pressure chemical vapour deposition using a new molecular precursor. This system offers a convenient method that delivers key structural requirements necessary to improve the thermoelectric efficiency of Bi2Te3 and to develop the nascent field of topological insulators.Thermoelectric

Two types of TiN/HfOx/TiN devices have been fabricated where the top 200nm TiN electrode has been deposited by two different sputtering methods; reactive, using a titanium target in a nitrogen environment, and non-reactive, using a titanium nitride target. Characterization of the materials shows that the reactive TiN is single-phase stoichiometric TiN with a sheet resistance of 7Ω/square. The non-reactive TiN has a sheet resistance of 300Ω/square and was found to contain significant amounts of oxygen. The resistive switching behavior differs for both devices. The reactive stoichiometric TiN device results in bipolar switching with a Roff/Ron ratio of 50. The non-reactive TiN results in unipolar switching with a Roff/Ron ratio of more than 103, however this device shows poor reproducibility. These results show that an oxygen rich layer between the top electrode and insulator affects the Roff value. It supports the theory of oxygen vacancies leading to the formation of conductive filaments.

A novel e-beam free, top-down spacer etch process was used to fabricate sub-hundred nanometer Ge2Sb2Te5 phase change nanowires. Naowires with a cross-section dimension of 50 nm × 100 nm (width × height) were obtained and phase change functionality demonstrated.

Cu/a-SiC/Au resistive memory cells are measured using voltage pulses and exhibit the highest ROFF/RON ratio recorded for any resistive memory. The switching kinetics are investigated and fitted to a numerical model, using thermal conductivity and resistivity properties of the dielectric. The SET mechanism of the Cu/a-SiC/Au memory cells is found to be due to ionic motion without joule heating contributions, whereas the RESET mechanism is found to be due to thermally assisted ionic motion. The conductive filament diameter is extracted to be around 4nm. The high thermal conductivity and resistivity for the Cu/a-SiC/Au memory cells result in slow switching but with high thermal reliability and stability, showing potential for use in harsh environments. Radiation properties of SiC memory cells are investigated. No change was seen in DC sweep or pulsed switching nor in conductive mechanisms, up to 2Mrad(Si) using 60Co gamma irradiation. All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Ge2Sb2Te5 (GST) phase change nanowires have been fabricated using a top-down spacer etch process. This approach enables controls over the dimension and location of the nanowires without affecting the electrical properties. Phase change devices based on these nanowires have been used to systematically investigate the contact resistance between GST phase change material and TiN metal electrodes. The specific contact resistance was found to be 7.96 × 10−5 Ω cm2 for crystalline GST and 6.39 × 10−2 Ω cm2 for amorphous GST. The results suggest that contact resistance plays a dominant role in the total resistance of GST memory device in both crystalline and amorphous states.

Amorphous silicon carbide (a-SiC) based resistive memory (RM) Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. All four possible modes of nonpolar resistive switching were achieved with ON/OFF ratio in the range 10 6-10 8. Detailed current-voltage I-V characteristics analysis suggests that the conduction mechanism in low resistance state is due to the formation of metallic filaments. Schottky emission is proven to be the dominant conduction mechanism in high resistance state which results from the Schottky contacts between the metal electrodes and SiC. ON/OFF ratios exceeding 10 7 over 10 years were also predicted from state retention characterizations. These results suggest promising application potentials for Cu/a-SiC/Au RMs

A versatile electrochemical system for the non-aqueous electrodeposition of crystalline, oxide free p-block metals and metalloids is described, and it is demonstrated that by combining mixtures of these reagents, this system is suitable for electrodeposition of binary semiconductor alloys. The tetrabutylammonium halometallates, [NnBu4][InCl4], [NnBu4][SbCl4], [NnBu4][BiCl4], [NnBu4]2[SeCl6] and [NnBu4]2[TeCl6], are readily dissolved in CH2Cl2 and form reproducible electrochemical systems with good stability in the presence of a [NnBu4]Cl supporting electrolyte. The prepared electrolytes show a wide potential window and the electrodeposition of indium, antimony, bismuth, tellurium and selenium on glassy carbon and titanium nitride electrodes has been demonstrated. The deposited elements were characterised by scanning electron microscopy, energy dispersive X-ray analysis and powder X-ray diffraction. The compatibility of the reagents permits the preparation of a single electrolyte containing several halometallate species which allows the electrodeposition of binary materials, as is demonstrated for InSb. This room temperature, ‘bottom-up’ electrochemical approach should thus be suitable for the one-pot deposition of a wide range of compound semiconductor materials.