Comprehension of the Behavior of Rectifier Diodes Through the In Situ Study of the Electrically Induced Phenomena on the Active Si Component

Nowadays, there are numerous advanced characterization techniques that offer great versatility in the field of materials. Concretely, confocal Raman microscopy (CRM) or techniques based on synchrotron radiation, such as single-crystal X-ray diffraction (SCD) are of major relevance for carrying out studies in solids. These non-destructive techniques allow exhaustive <i>in situ</i> structural analysis at the local scale of several materials, without the need for very specific sample preparation, and achieving high spatial resolution.<br/>Located <i>in situ</i> structural studies are of great utility in the semiconductor-based technology field. One of the main limiting factors of these devices is the modifications that may take place on their structure as a consequence of the high electrical current that flows through them when they are in operation. Press-fit rectifier diodes are an application example of Si-based electronic devices, which have a great interest in the automotive industry. Thanks to their ability to allow the current to flow in one direction only and blocked it in the opposite one, they are often employed to transform the alternating current produced by the alternator into a direct current, in order to make it suitable for the power supply of the vehicle. At <i>in operando </i>conditions, diodes endure electrical current in the order of tens of A, which leads to the overheating of the device by the Joule effect at temperatures about 250 ^oC. This fact may pose a problem, not only because of the thermal degradation of the devices but because of the appearance of structural damage associated with their multicomponent nature. Rectifier diodes are commonly composed of several materials: a silicon semiconductor wafer where the rectifier technology is located, joined to a copper heat-sink and to an epoxy region, whose function is to provide mechanical and electrical protection. Their thermal response is different for each one, leading to the appearance of mechanical stress as a consequence of the mismatch of the thermal expansion coefficients. In addition, other structural variations that the electric current may induce on the active Si, which can influence the behavior of the diode, such as carrier dynamics, may also take place on the devices at <i>in operando</i> conditions.<br/>In order to optimize the performance of the diodes, it is essential to know their behavior and the different phenomena occurring during their operation. For that, in this work, an <i>in-situ</i> characterization has been carried out using different techniques. First, a preliminary study of the thermal response of the whole diode by infrared thermography revealed the inhomogeneous heating of the device. Then, the structural modifications that the active semiconductor undergoes were evaluated by confocal Raman microscopy and X-ray diffraction in synchrotron (ESRF, Grenoble). Results have allowed discerning the influence of the heating phenomenon caused by the Joule effect from other non-purely thermal phenomena, characteristic of these devices, as well as to identify the presence of different regions located in the Si, whose differences are based on the stress and doping scheme of this component. Experiments were carried out in diodes with different technologies (Schottky, MOS and PN) and proceeding from different providers (different designs), intending to evaluate the influence of different parameters. The study was useful to comprehend the phenomenology induced on the active Si region of rectifier diodes in working conditions in order to increase their useful life by reducing their failure rate.