Interfacial Space Charge Testing System With High Resolution Based On New Kinds Of THz Devices

Properties of the space charege in the heterostruture interface are the foundations of material application and device fabrication. The measuring for the distribution and status of space charge is the active research content for along time. The highest resolution can be 1 μm. With the fast development of organic electronic devices, MEMS, and nano materials, however, the information of the space charge can not be wholly achieved through existing measuring methods especially at small scale. The information lack leads to the stagnation of theoretical and experimental research on complex interfaces. Nowadays, this problem might be resolved with the help of the appearance and development of terahertz(THz) wave. But the development is limited largely by bad EO properties and bad stabilities of THz devices. New kinds of devices are designed and manufactured based on electro-optic(EO) polymers in this paper. With the help of them, the excitation and detection of THz wave are realized. Combined with Elastic-optic sampling technique, Distribution measurement for space charge with high resolution is also realized. The main research is as follows:The concept and composition plan of polymer with double EO molecules were introduced. One kind of the chromophoric group was grafted to the polymer main chain by a chemical method to form the side chain EO polymer. Then another small NLO molecule, ethyl 4-(dimethylamino) benzoate(EDB), was mixed into the polymer by physical method to improve EO properties. The structures of the products were characterized and EO coefficients were tested. According to the results, two kinds of samples were selected for further optimization. The effect on EO coefficient by different EDB mixing proportion and different polarization temperature were investigated. Experimental result shows that the enhanced EO coefficients for the two samples can be 46.7 pm/V and 69.1 pm/V respectively under the suitable conditions, which reduce to 61% and 69% of their initial values after 600 hours.New kinds of THz wave detecting devices with interdigitated coplanar electrodes structure were designed and manufactured. The normal incidence of THz wave was feasible because of the alternation of polarization electric field, which lead to the disappearance of the effect on detectivity by incident angle. Experimental result shows that the structure change of the devices has no effect on the EO properties of the material. While detecting the same THz signal, the amplitude of device with interdigitated coplanar electrodes structure was bigger than that of device with sandwich structure. The ratio was about 1.15:1.The excitation and detection system of THz wave was established. Based on carbazole polyphosphazene grafted with 2,4-dinitroaniline and ZnTe crystal, detecting devices with both sandwich structure and interdigitated coplanar electrodes structure were manufactured. With the help of these devices, the time domain waveform of THz wave was obtained. Compared with the ZnTe crystal, the detection efficiency and the spectrumsensitivity of polymer with double EO molecules could be enhanced by 28.9% and 67.3% respectively. The polymer devices have more advantages over inorganic crystal ones.The elasto-optical sampling senseor was designed and manufactured. The data extraction and measurement for elastic wave signals by optical method was realized. The operating principle of the sensor was stress birefringence. The time domain informations could be obtained through the polarization state measurement of the detecting pulse with the help of optical-mechanical delay lines. The polymer film could be polarizated without the alternation of the device structure. The sensor had fine sensitivity and stability, whose properties remained unchanged for one year time.A new testing system with high resolution was established. The pulse voltage was subtituted by THz wave as excitation and the piezoelectric sensor was subtituted by elastic-optic sampling sensor as response. The system had fine stability and there were no limit and special requirement for the sample to be tested. A silicon PN junction sample was tested under the equilibrium state, forward state and reverse bias state. The width of the PN junction was obtained, which was 9nm when the bias voltage was about 0.65 V. Then, the width remained unchanged although the bias voltage still became larger, which agreed very well with the characters of the silicon PN junction.