Study On The Key Problems Of Ultra-fast Photoconductive Switch And Its Testing System

Thin titanium film can be oxidized completely with scanning probe microscope (SPM) via anodic oxidation to form Metal-Insulator-Metal (MIM) structure to fabricate various nanometer scale electronic and opto-electronic devices, such as such as single electron transistor (SET), high electron mobility transistor, single electron memory (SEM) and photoconductive switch. Ultra-fast photoconductive switch has extensive application in the field of ultra-fast devices testing and optical communication. The key problems of design and theoretical calculation of ultra-fast photoconductive switch, preparation and characterization of substrate material, and characteristic measurement of the fabricated prototype device were extensively studied in this dissertation. The research work mainly includes five aspects as follows: 1. The substrate materials of nano electronic and nano opto-electronic devices were compared and selected. From analyzing, O+ implanted silicon on sapphire was chosen as the substrate, oxidation titanium line fabricated on ultra-thin titanium film with AFM anodic oxidation as the functional part and coplane strip geometry as the transmission line of photoconductive switch to form a novel ultra-fast photoconductive switch. The approximate numerical value of output characteristic of the designed novel device was solved. 2. Fabrication and testing methods of nano thin film were developed. Ultra-thin titanium film was deposited with dual facing target sputtering system, the accurate thickness of the film was measured with bench-top stylus profiler, the surface flatness of the film was measured with AFM and the I-V curve of the film was measured with STM. The measured results indicated that the deposited titanium film was very flat and homogeneous and it had excellent conductivity. The compositions of the film were characterized with XPS and the thickness of the film obtained from XPS result was consistent well with the deduced result by bench-top stylus profiler. 3. Experiments of AFM anodic oxidation of Ti film under various conditions were extensively carried out and relevant theoretical modeling was deduced based on present theories. The proper conditions to perform AFM oxidation of titanium were biased voltage of 8V, scanning speed of 0.1μm/s and relative humidity of 30%~50%. Under such conditions, six nano-oxidation titanium lines 5μm long were fabricated from left to right at every 1μm separation which indicated that those nano-oxidation lines had the excellent consistency of the height, width and linearity. 4. Structure design and fabrication process of novel photoconductive switch were carried out. Three masks were designed and prepared to form transmission lines and electrodes of ultra-fast photoconductive switch. The transmission lines, electrodes, functional gap of ultra-thin titanium film and oxidation titanium lines were fabricated with micro-electronic optical lithography, dual facing target sputtering and AFM anodic oxidation to form a prototype of ultra-fast photoconductive switch. The dark I-V characteristic of the ultra-fast photoconductive switch was measured. 5. Performances testing methods of novel photoconductive switch were developed. A set of ultra-fast electro-optic sampling system based on femto-second laser was designed, its temporal resolution and spatial resolution were analyzed and its minimum detectable voltage, signal-to-noise ratio and dynamic range were calculated. Motion controlling of stepping motor for optical delay line and data acquirement from lock-in amplifier were performed. Auto correlation measurement system of ultra-fast photoconductive switches was designed.