Nanostructuring Ferroelectrics via Focused Ion Beam Methodologies

As we reach the physical limit of Moore’s law and silicon based electronics, alternative schemes for memory and sensor devices are being proposed ona regular basis. The properties of ferroelectric materials on the nanoscale are key to developing device applications of this intriguing material class, and nanostructuring has been readily pursued in recent times. Focused ion beam (FIB) microscopy is one of the most signi cant techniques for achievingthis. When applied in tandem with the imaging and nanoscale manipulation afforded by proximal scanning force microscopy tools, FIB-driven nanoscale characterization has demonstrated the power and ability which simply may not be possible by other fabrication techniques in the search for innovative and novel ferroic phenomena. At the same time the process is not without pitfalls; it is time-consuming and success is not always guaranteed thus often being the bane in progress. This balanced review explores a brief history of the relationship between the FIB and ferroelectrics, the fascinating properties it has unveiled, the challenges associated with FIB that have led to alterna- tive nanostructuring techniques and nally new ideas that should be explored using this exciting technique

Scaling of electroresistance effect in fully integrated ferroelectric tunnel junctions

Systematic investigation of the scalability for tunneling electroresistance (TER) of integrated Co/BaTiO3/SrRuO3 ferroelectric tunnel junctions (FTJs) has been performed from micron to deep submicron dimensions. Pulsed measurements of the transient currents confirm the ferroelectric switching behavior of the FTJs, while the hysteresis loops measured by means of piezoresponse force microscopy verify the scalability of these structures. Fully integrated functional FTJ devices with the size of 300×300 nm2 exhibiting a tunneling electroresistance (TER) effect of the order of 2.7×104% have been fabricated and tested. Measured current density of 75 A/cm2 for the ON state and a long polarization retention time of ON state (\u3e10 h) show a lot of promise for implementation of high-density BaTiO3-based FTJ memory devices in future

Fabrication of air-bridges for qubit design

Superconducting quantum electrical circuit based on Co-planar waveguide technology is considered one of the most promising candidates for practical realization of a quantum computer in future. For purpose of designing a multi-qubit quantum processor which is the heart of a quantum computer, it is required to couple qubits to a large number of superconducting transmission lines and resonators. Placing all these transmission lines and resonators in a practical design unavoidably creates bending and discontinuities in the ground planes which have higher order parasitic modes that can be excited. These undesired parasitic modes are detrimental for quantum measurement, for example during readout of a qubit. Unwanted modes can easily interfere with a resonator frequency when coupling to the qubit. These parasitic modes can propagate throughout CPW structure and make unequal ground potential at the corresponding ground planes. The easiest way to suppress these parasitic modes is to connect two unequal ground potential with superconducting air-bridges in order to bring them under equal potential in superconducting state. However, connecting airbridges on top of CPW adds shunt capacitor which may cause undesired reflection in the CPW. In this thesis work, we designed superconducting air-bridges on top of superconducting CPW transmission line which is a subsystem of large quantum electrical circuit. Our focus was to reduce added shunt capacitance by choosing the right height of these air-bridges. To keep the reflection coming from the air-bridge at minimum level, an airbridge height of 8.5μm~15μm was chosen. The performance was verified by EM simulation and these heights were selected for device fabrication. We developed a new fabrication method for processing 8.5μm~15μm high aluminum air-bridges for quantum electrical circuits. The method is compatible with the quantum circuit and easily reproducible. Finally, input reflection measurement (S11) at cryogenic temperature was performed for 8.5μm high, 300μm long aluminum air-bridges with aluminum CPW transmission line. Negligible amount of input reflection (S11) was observed from these measurements which is consistent with the result of EM simulation

Contact resistance to SrRuO\u3csub\u3e3\u3c/sub\u3e and La\u3csub\u3e0.67\u3c/sub\u3eSr\u3csub\u3e0.33\u3c/sub\u3eMnO\u3csub\u3e3\u3c/sub\u3e epitaxial films

Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and LSMO films after exposure to plasma treatment. Severe contact resistance degradation was observed for Ti contacts as compared to Pt after reactive ion etching on LSMO films. The effect of oxygen (O2) plasma on LSMO was observed to be most severe with non-ohmic behavior with Ti contacts, which can affect the functionality of FTJ devices. Finally, the thermal stability of contacts was investigated, Pt contacts to SRO show low resistance ohmic behavior even after annealing at 900°C, making it a suitable contact for FTJ devices

Fabrication of large dimension aluminum air-bridges for superconducting quantum circuits

Proper grounding between different ground planes in coplanar superconducting qubit circuits is important to avoid spurious resonances which increase decoherence. Here, the authors present a possible solution to suppress such undesired modes using superconducting aluminum air-bridges which have been fabricated on top of aluminum coplanar waveguide transmission lines. 3D electromagnetic simulations were done to guide the design of the air-bridges such that the input reflection (S11) of the bridges was kept at a minimum level. A fabrication method based on optical lithography techniques was developed and it resulted in air-bridges with a height of approximately 10 μm and lengths of up to 500 μm. The method can be generalized to arbitrary length air-bridge with heights even exceeding 15 μm