QUALITY EVALUATION OF AGRICULTURAL MACHINERY SENSORS FROM THE ANALYSIS OF THE LEAKAGE CURRENT IN ALUMINUM CONTACTS
Authors: Каширин Д.Е. , Левина Т.А. , Глухих Я.М. , Клочков А.Я. , Честных А.Р. 
Published: December 2023

Проблемы и цель. Актуально и необходимо увеличить срок эксплуатации датчиков, применяемых в сельскохозяйственной технике, что связано с проверками и анализом фактических характеристик датчиков. Естественно, с точки зрения надёжности контроля параметров сельскохозяйственной техники, представляет интерес в применяемых датчиках зависимость относительной деградации начального входного сопротивления и выходного сигнала Изменение входного сопротивления и начального выходного сигнала датчика определяется характеристиками элементов микросхем, которые зависят от деградации их входных и выходных элементов, включая алюминиевые контактные области. Эти изменения происходят при определённых температурах, степени и времени нагрузки самих датчиков. Материалы и методы. На электрофизические свойства датчиков наибольшее воздействие оказывают токовые нагрузки. Причем механизм влияния на утечки токов заключается в основном в образовании структурных дефектов и структурного превращения границ раздела металлизации к поверхности полупроводника [1]. С повышением уровня легирования влияние этих эффектов ослабляется [2]. Измерялись токи утечки структуры при различных напряжениях смещения. Только те контактные цепочки сопротивления, которые отклоняются друг от друга менее чем на 2,0 %, нагружали параллельно для данного цикла нагрузки, который длился около 15мин. Во время экспериментов на тестовых структурах температура при измерениях токов утечки различных контактов стабилизировалась с точностью до ±2,0⁰ С. Результаты. В смоделированных условиях эксплуатации контактов датчика в тестовых структурах (Al(Si) контактов к слоям n+ Si и p+Si) при постоянном напряжении питания контактов чувствительность после воздействия токовых и температурных нагрузок уменьшилась примерно в 2,0 раза. Проведенные исследования показали, что при 25о С тестовые структуры работоспособны до уровней воздействия токов 5 мА. Возникающие изменения характеристик контактов до уровней токов 10 мА могут быть в определенной степени учтены благодаря тому, что наблюдалась хорошая повторяемость результатов нашего эксперимента. Заключение. Прекращение утечки наблюдается в n+ Si контактах, но, несмотря на Si миграцию, величина утечки перехода не поддаётся снижению в контактах Al(Si) к p+Si слоям. В Al(Si)-n+ Si контактах; среднее время прекращения тока утечки (СВПТУ) имеет энергию активации Ea =0.8 эВ и обратно пропорционально плотности тока на проводящем крае контакта. Таким образом, управляя технологией получения алюминиевого контакта и формирования его к поверхности полупроводника, можно увеличивать и прогнозировать срок службы датчиков при эксплуатации сельскохозяйственной техники.
Problems and purpose. The control of the speed of rotation of shafts and drums on agricultural machinery is necessary to adjust the speed of rotation of seeders, harvesters, reels and other actuators for the processing of various crops, the control in ecology is also necessary to control environmental parameters, such as electromagnetic fields and other measurements are carried out using sensors. It is urgent and necessary to increase the service life of agricultural machinery sensors, that is connected with checks and analysis of the actual characteristics of the sensors. As a rule, they have the same functional purpose, package and type of outputs and differ only in sensitivity, response speed and power consumption and the type of microcircuits. The key features of all agricultural equipment in which these microcircuits can be applied are compactness and stringent requirements for operation and power consumption. Naturally, from the point of view of the reliability of monitoring the parameters of agricultural machinery, it is of interest in the sensors used to depend on the relative degradation of the initial input resistance and output signal Changes in the input resistance and initial output signal of the microcircuit are determined by the characteristics of the microcircuit elements which depend on their degradation of the input and output elements including aluminum contact areas. These changes occur at certain temperatures, the degree and time of loading of the sensors themselves. Materials and methods. Let us dwell in more detail on the analysis of the leakage currents of aluminum contacts, which are used in the converters of any agricultural sensor. It is known that the resistance of converters (semiconductor devices) to temperature effects depends on the level of doping, defectiveness of the semiconductor material, etc. The electrical properties of semiconductors are most affected by current loads. Moreover, the mechanism of influence on current leakage is mainly in the formation of structural defects and structural transformation of the metallization interfaces to the semiconductor surface [1]. With an increase in the doping level, the influence of these effects weakens [2]. We measured the contact characteristics before exposure to significant temporary and current loads and after prolonged exposure to these loads on aluminum contacts in the temperature range of 100–252 ⁰C. Leakage currents of the structure were measured at various bias voltages. Only those resistance contact strings that deviate less than 2.0 % from each other are loaded in parallel for this load cycle, which lasts about 15 minutes at a reverse voltage of 10 volts. During experiments on test structures the temperature during measurements of the leakage currents of various contacts stabilized with an accuracy of ±2.00 ⁰С. Results. In our moderate impacts on these sensors they amount to a decrease of about 20% of the nominal value of the specified characteristics, and at 150 ⁰C the resistance increases by 4 times. Under simulated operating conditions of sensor contacts in test structures (Al(Si) contacts to n+ Si and p+Si layers) at a constant contact supply voltage, the sensitivity after exposure to current and temperature loads decreased by about 2.0 times. When exposed to extreme conditions (temperature, current) of contact operation and the impact of the load time of these structures, depending on the type of contact, the resistance of the sensors increases to infinity.Our studies have shown that at 25°C the test structures are operable up to the levels of exposure to currents of 5mA. The resulting changes in the characteristics of the contacts up to current levels of 10mA can be taken into account to a certain extent, due to the fact that a good repeatability of the results of our experiment was observed.The same proportional changes in the characteristics of the contact occurred when measuring the output signal of the sensor, which was determined by the degradation of the aluminum contacts of the output elements (transistors) of the microcircuit. The output signal of the sensor may depend on the model and type of converter (microcircuit), but, as a rule, is in the range of 0.5-1.0 V which is in good agreement with our result. Conclusion. It has been established that the silicon migration in semiconductor test structures is observed in Al(Si) contacts to n+ Si and p+Si layers. Each pit is located near the leading edge of the metal of the most negatively biased contacts. The cessation of leakage is observed in n+ Si contacts, but, despite Si migration, the increase in junction leakage cannot be reduced in Al(Si) contacts to p+Si layers. In Al(Si)-n+ Si contacts the mean leakage current termination time (MTCT) has an activation energy of Ea=0.8eV and is inversely proportional to the current density at the conductive edge of the contact. The parameters of current compression and effective current are determined which makes it possible to predict SVPTS from contacts and technological scaling. In typical cases the compression of the current is so strong that at constant current changing the length of the contact has little effect on the THC. Thus, by controlling the technology of obtaining an aluminum contact and forming it to the surface of a semiconductor it is possible to increase and predict the service life of sensors. We concluded that in order to increase the service life of sensors, it is necessary to improve the design and technological base of the converters and it depends on the operating conditions of agricultural machinery.