Electro-optic Probing Technique With Ability Of Voltage Calibration For EO Signal

In the last 20 years, with the development of the design andfabrication technology for integrated circuits (ICs), the microelectron-ics chip has been integrated from LSICs (large scale ICs) to VLSICs(very large scale ICs). In order to solve the uncertainty problems insideICs chip such as creepage, heat effect, S'parameter and modelparameter, the design and fabrication technology of ICs need to beameliorated urgently. When producing the ICs chips, the larger thearea of ICs chip is, the larger the error possibility is. At present, hardlyany ICs chip manufacturer's error ratio is under 50%. Though thelarger chips have further space, it will be not worth the candle if suchchips cannot work. In the point of view of Statistics, the finishedproduct ratio of a sort of device is also the ratio of unmistaken working,or we can say it is the device's reliability. Some better device also maybe obtained by strict filtration procedure, but the un-reliability hiddentroubles caused by low finished product still consist in the deviceobtained by filtration procedure. It is impossible that the reliability ofthe device with low finished product is increased by certain kindfiltration procedure. And the device with high reliability is justfabricated by the high reliability design and technique.In order to ameliorate the design and fabrication technology in theinvestigation process, the inside characterization of ICs chip obtainedin the investigation process need to be analyzed and diagnosed. Atpresent, the applied check equipments are mostly listed as follows:Probe needle method, E-beam probing or scanning electron micro-scope method, Photoemissive sampling method, Photoconductivityswitching sampling technology, Radiation microscope (PHEMOSseries) and Electro-optic Probing method. All the three kinds ofmeasurements mentioned above have not yet satisfied the needs of thestudy and the developing of ICs because of their limitations. It is aimportant problem to ameliorate the Electro-optic sampling technique,and make it a kind of handy equipment applied in microelectronicschip inside characteriza-tion analysis at all times.The external EO probing technique overcame the limitations of thesubstrate materials, but brought new issues at the same time: first, ininternal EO probing technique the substrate materials contact down tothe signal transmission lines, the signal electric field can extend intothe EO materials completely and distribute uniformity. For externalEO probing technique, the separation between EO crystal and signaltransmission lines product the air gap when the circuits to be tested.Here, the huge difference of the dielectric constant between EOmaterial and ambience make the electric fields compressed in the airgap, only few part of the electric fields can extend into the EO crystal,so EO signal amplitude be reduced largely. For the same signaldetection and amplification system, this means the voltage sensitivityis reduced. In the typical EO crystals, LiNbO3 and LiTaO3 havebiggish EO coefficient (γ33=30.8 and 30.3 pm/V respectively), andtheir relative dielectric constant is 28 and 43 respectively, witch islarger than that of air further. Second, the tested EO signal is the un-distortion simulation of the voltage signal in the ICs, and the signalwave, the time and phase relaxations of the wave all accord to theelectric signal in ICs completely. But the amplitude of EO modulationsignal lies on the lognitudinal component of the electric field issuedfrom the electric signal transmission line;witch is influenced by theneighbor circuit layout. Third, the most fundamental work for the practical ofexternal EO probing system is that the investigation and manufacture ofprobe tip material with thermally stability and large EO coefficient. Allof the EO probing systems reported by foreign investigators utilizedinorganic EO crystal as the detector of modulation electric fields. Forinternal EO probing system, mentioned above, its application islimited by the substrate materials. So the calibration voltagemeasurement cannot be realized.This paper simulates the electric potential distribution and theelectro-optic (EO) signal amplitude in a longitudinal poled EOpolymer external probe tip on the electric signal transmission linesunder test. The influence of the circuit layout on the EO probing isdiscussed. A novel probing configuration with a poled polymer EOprobe tip is built and demonstrated for the first time, by which thesignal voltage level corresponding to the EO signal can be calibrated.Using the new probe tip, we examine the influence of the variations ofthe linewidth and the spacing between neighboring lines on the EOsignal. The results indicate that when the vertical distance between thetested point on the lines and the reference electrode is not larger thanthat between the tested point and its neighboring conductor, thedisturbance from circuit layout can be avoided so that the voltagecalibration of EO signal can be carried out.This paper designed and fabricated a novel EO probe tip: anantireflectivity (AR) coating is evaporated onto the top surface oftransparent substrate and an electric film is evaporated onto anothersurface, the electric film has about 30% reflectance ratio on probingbeam. An organic EO film is spin-coated onto the electric film. Whenprobing the tested points, the electric film is grounded and the probetip stands freely onto the transmission lines. As long as the verticaldistance between the tested point on the lines and the referenceelectrode is not larger than that between the tested point and itsneighboring conductor, the electric field issued from the electric signaltransmission line and extended into the EO material, terminated in thegrounded electric film completely. Here, the disturbance from circuitlayout can be avoided so that the voltage calibration of EO signal canbe carried out.In the EO probing method mentioned above, the configuration ofprobing tip, the fabrication of EO film and the transform from phasemodulation to amplitude modulation of the probing beam are alloriginal creation of this paper.This paper designed and fabricated GSG coplanar microstrip circuit,and the equivalent impedance of the transmission line is 50Ω . In orderto satisfy the different requirement of circuit layout, there are twokinds of transmission line configuration: one is the case of thelinewidth equal to the spacing and the smaller width is 1μm;another isthe case of the various spacing and the linewidth are all 5μm, thesmaller spacing is 1μm. This paper finished the calibration voltagemeasurement by utilizing poled polymer film as external probe tip, andthe measurement result coincides basically with the simulations. It isthe first time that this experiment is finished in the EO probing domainall over the world.This paper fabricated the organic\inorganic EO material utilizing thesol-gel technique. The chromophores Disperse Red 1(DR1) is dopedinto the oxide matrix, the best concentration of solution and theheating treatment condition has been obtained by experiments. Thelarge EO coefficient of γ 33=56pm/V was obtained and the value wasunvaried at room temperature, If we selected the poling temperature,the EO coefficient of γ 33=30pm/V was obtained and the value wasstable at 80oC for 1000h.