The Development Of Organic Magnetoresistance And Brightness Variation Measuring Instrument

In recent years, organic semiconductor materials are widely concerned.It appears enormous potential for development in many areas with manysignificant advantages and new features. Such as the good photoelectricityperformance, the simple production method, the low manufacturing cost,the wide range of materials, the soft mechanical property and so on.Organic Electroluminescence technology is currently the most importantapplication of organic semiconductor materials. Through the organic lightemittingdevices and materials research, the researchers found some newphenomena, including the organic magnetoresistance effect and thephenomenon of brightness variation caused by magnetic field. Depth studyof the essence behind these phenomena is very important for us to exploremore great organic materials, develop more high-performance organicsemiconductor devices and even build the perfect organic optoelectronicsand organic magnetoelectronics.This paper designs a kind of automated measuring and controllinginstruments which is used to measure and analyze the magnetoresistanceand brightness variation of organic electroluminescence devices. It canprecisely control and monitor the magnetic field environment and real-timemeasure the magnetoresistance and brightness variation of organicelectroluminescence devices, then transfers the data to PC to do the dataprocessing and imaging.The instrument consists of three parts: the magnetic fieldmeasurement and control part with the core of 51 MCU, the parametersmeasured part with Keithley Multi-Channel System SourceMeter and the platform of controlling, displaying and data processing which is based onPC.Among them, the magnetic field measurement and control part includethe main control circuit, the opto-isolation circuit, the electromagnet currentfeedback circuit, the magnetic field monitoring and display circuit, the serialcommunication interface circuits, the power main circuit, the electromagnetand so on. The main control circuit to AT89C52 MCU as the core andinclude digital potentiometer AD5263 and phase-controlled trigger circuitand so on; Electromagnet current feedback circuit probe output currentwith Hall current sensor LA28-NP. Then convert it to the voltage signal withsampling resistor. Then feed it back into the control circuit throughconditioning circuit and amplifier circuit; Magnetic measuring is realizedthrough Hall probes and constant current source. The voltage signal isamended by Allelic voltage compensation circuit. Then through programcontrolledadjustment and enlarge circuits, put it into ADC MAX110.MAX110 convert it into digital signal, Then transmit it to AT89C52, whiledisplay magnetic field values with LCD1602. We use MAX232 converterchip to do the serial communication.It can convert the TTL electric levelsignals to the RS-232C electric signals to achieve the communicationbetween the instrument and PC. The PC is used to set the workingparameters and magnetic field scan mode and so on; The main circuitinclude the controlled part of the phase-controlled trigger circuit, bridgerectifier circuit, filter circuit, programmed switch and the magnetic fielddirection transform circuit which is composed of SCR; We use optocouplersto insulate digital circuits and analog circuits. We use TLP521 in the lowfrequency interfaces and use 6N137 in the high frequency interfaces sothat it can enhance the reliability of the circuit.The parameters measured part of organic electroluminescence device samples for Keithley 2612 Multi-Channel System SourceMeter as the mainbody. A channel provides bias voltage and collects the current and voltagesignals of devices to get the magnetoresistance data. Another channelcoordinates with the optical powermeter probe (Optical powermeter orphotomultiplier) to collects the light signal to get brightness variation data.Then the Keithley sourcemeter transfers the measured data to PC viaGPIB-to-USB interface cable.The PC software platform is written in Visual Basic 6.0 andMeasurement Studio 6.0.It can not only set the instrument's systemparameters, working methods and scanning mode easily, but also real-timedo the data processing and imaging of the measured data. It can help useranalysis problems efficiently.MCU monitoring program is written in assembly language. It includesthe main program, interrupt service subroutine, control subroutines set,LCD display subroutine and serial communication subroutine and so on.Through the practical application of customer, it is proved that theinstrument is stable, powerful, easy operation and high degree ofautomation. The control precision of the magnetic field can reach±0.3%.The minimum resolution of magnetic field monitoring is 0.1Oe. Theparameter measuring accuracy is better than±0.1%. It fully achieves thedesired purpose and accuracy of measurement. It can greatly improve theR&D efficiency of organic electroluminescence device.