Study Of The Radio Frequency Single Electron Transistor Probe And Its Applications

With the rapid research progress on solid-state quantum information devices, nanodevices and novel nano functional materials, high speed, high sensitivity and high spatial resolution charge sensing is required. Conventional low-temperature voltage or current amplifiers cannot satisfy these testing requirements due to the following limitations. Firstly, the large power consumption of amplification circuit may cause large temperature disturbance to the measured objects at low temperatures. Secondly, their sensitivity and speed are low. Finally, the detection circuit is usually integrated with the device under test(DUT). Thus the location of the detection circuit is fixed and unable to adjusted, leading to poor testing flexibility, low efficiency, and uncontrollable back action on the DUT.The radio-frequency single electron transistor(RF SET) scanning probe investigated in this thesis can effectively resolve the above-mentioned problems, which can be used to map charge distribution and sense dynamic charge fluctuation at any places in nanodevices or circuits under test, realizing a high speed, high sensitivity and high spatial resolution charge detection. It can serve as a certain oscilloscope or scanning probe microscope in the studies of physics, materials, devices and circuits in micro-nano scales. By integrating an SET on the tip of the insulating probe, the high spatial resolution charge distribution imaging and geometric imaging can be realized. By integrating the RF resonance circuit on the main part of the insulating probe and reading out the charge state of the SET through the RF resonant reflection signal, the low speed disadvantage of the traditional SET is overcomed, and the high speed and high sensitivity charge detection function can be achieved. These integrations are technical challenges of the nanofabrication and low-temperature operation of probes. The development of the proposed RF SET probe provides an important testing instrument with high charge, time and spatial resolutions for investigating nanodevices, quantum electronic devices and their integrated circuits. The focuses of this thesis are the integrated fabrications of SET, RF resonance circuit and scanning probe based on the silicon-on-insulator(SOI), and the realization of high operating temperature and large temperature range. The main research content of this thesis is summarized as follows.Firstly, the analytical current-voltage(I-V) model has been established based on the orthodox theory of SET as an ultra-sensitive electrometer. The SET is simulated by combining the Monte Carlo(MC) method with the Master Equation(ME) method. Simulation results with higher precision and faster convergence are obtained. Effects of the gate voltage, drain voltage, temperature, and tunneling junction resistance on electrical characteristics of the SET are analyzed in details. Effects of these parameters on the sensitivity of SET are particularly investigated, and the design criteria for SET electrometers are summarized, providing important guidance for designing SETs on the subsequent RF SET probe.Secondly, unique SET design and fabrication techniques based on highly doped SOI are developed with advantages of good structure and size controllability, allowing reliable fabrication of Si SETs. In particular, methods of image reversal and region dividing are developed. Combining with electron-beam lithography, inductively-coupled plasma etching, UV lithography, and thermal oxidation, the controllable Coulomb island and tunneling barriers of SET are obtained. With a Coulomb island of 60 nm in diameter and a charging energy about 12.5 meV, the Si SET shows obvious drain current oscillations at operation temperatures up to 70 K. The oxidation process not only forms high quality SiO2 tunneling barriers, but also further reduces the effective size of the quantum dot, helping to improve the working temperature of the SET. Compared with Al/Al2O3 SETs and GaAs/AlGaAs SETs, the fabricated Si SET has increased its working temperature from the order of mK to K.Thirdly, the equivalent circuit models of the transmission and reflection RF SETs are established. Effects of the charge-modulated impedance of SET on the quality factor, impedance and RF signal of the RF resonance circuit are investigated. The optimum matching of the SET impedance, resonant frequency, quality factor and the sensitivity of the SET impedance are obtained. Comparisons indicate that the transmission RF SET has higher resonance frequency and quality factor, while the reflection one shows a higher sensitivity. RF readout circuits are also improved and designed, realizing simultaneous measurement of RF and electrical properties, which can provide practical guidances for optimizing RF SET circuit and realizing high speed and high efficiency readout of RF SET signals.Fourthly, the simplified equivalent circuit of the SET for charge sensing is established. The effects of the distance between SET and the probe tip on the response and sensitivity of RF SET probe are studied, and the design rules of the RF SET probe are developed. Furthermore, based on the developed SET fabrication technique, a novel RF SET scanning probe is successfully fabricated with an integrated SET locating a small distance away the tip and radio transmission lines integrated on the body of the scanning probe using the unique radio-frequency SOI substrate, which reduces the RF signal loss efficiently. By further optimizing the design and improving the fabrication process, the SET is precisely located and fabricated on the probe tip without potential harms during the probe etching. The fabricated Si SET with a Coulomb island of about 70 nm in diameter is located about 10 ?m away from the probe tip, exhibiting obvious Coulomb blockade phenomenon at 4.2 K. The best charge sensitivity of this probe is in the order of 2.5?10-5 e/Hz1/2. The charging energy is about 18 meV, and the theoretical operating temperature is up to 208 K, provding a wide working temperature range. By integrating the RF SET probe to the readout circuit, the transmission and reflection signals are mearsured. The resonant frequencys of the transmission and reflection signals are 828 MHz and 690 MHz, respectively, while the quality factors of the transmission and reflection RF SETs are 7.0 and 6.4, respectively.Finally, by integrating the RF SET probe with the subsystems including the low-vibration and low-temperature vacuum systems, the radio frequency readout circuit and the scanning control system, the RF SET probe scanning detection and oscilloscope system based on the RF SET probe is completed, which can fulfill the surface scanning function. Besides, a charge sensing model of the RF SET probe is developed using the electrostatic module of COMSOL. Effects of the bias and detection distance on the potential of Coulomb island are studied by electrostatic field analysis. The relationship between the coupling efficiency and the sensing distance is investigated, and a quantitative analysis method of charge sensing is developed. Then, the voltage sensitivity and spatial resolution of the probe are evaluated. A voltage sensitivity as high as 10-6 V/Hz1/2 and a spatial resolution better than 100 nm can be achieved. Finally, a two-dimension potential distribution map of a quantum dot is obtained. This analysis method provides the first-hand guidance for signal analysis and quantitative charge test of charge detection systems.