Humidity sensitivity of large area silicon sensors: Study and implications Fernández-Tejero, J.; Allport, P.P.; Aviñó, O. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Volume:
978, Issue:
C
Journal Article
Peer reviewed
Open access
The production of large area sensors is one of the main challenges that the ATLAS collaboration faces for the new Inner-Tracker full-silicon detector. During the prototype fabrication phase for the ...High Luminosity Large Hadron Collider upgrade, several ATLAS institutes observed indications of humidity sensitivity of large area sensors, even at relative humidities well below the dew point. Specifically, prototype Barrel and End-Cap silicon strip sensors fabricated in 6-inch wafers manifest a prompt decrease of the breakdown voltage when operating under high relative humidity, adversely affecting the performance of the sensors. In addition to the investigation of these prototype sensors, a specific fabrication batch with special passivation is also studied, allowing for a deeper understanding of the responsible mechanisms.
This work presents an extensive study of this behaviour on large area sensors. The locations of the hotspots at the breakdown voltage at high humidity are revealed using different infrared thermography techniques. Several palliative treatments are attempted, proving the influence of sensor cleaning methods, as well as baking, on the device performance, but no improvement on the humidity sensitivity was achieved. Furthermore, a study of the incidence of the sensitivity in different batches is also presented, introducing a hypothesis of the origins of the humidity sensitivity associated to the sensor edge design, together with passivation thickness and conformity. Several actions to be taken during sensor production and assembly are extracted from this study, in order to minimize the impact of humidity sensitivity on the performance of large area silicon sensors for High Energy Physics experiments.
The behavior of the barrier height of the SiC/SiO 2 interface has been investigated over a wide temperature range, from 173 K to 523 K. These data complement the literature, providing a better ...knowledge of this parameter, which was studied only over a more restricted temperature range, and never before for low temperatures. It is highlighted that the measured samples exhibit a barrier height temperature dependence very near to the theoretical one (≈-0.7 meVK -1 ). Beyond 473 K, the barrier height seems to drop faster for some samples, reaching ≈-1.4 meVK -1 . If this faster decreasing rate is maintained for higher temperatures, it could limit 4H-SiC MOSFETs performances or reliability for high-temperature applications. It is expected that the data provided here will allow for more accurate modeling of the gate current and the charge injection in the oxide layer of power MOSFETs, leading to more reliable predictions of the oxide lifetime for 4H-SiC MOSFETs.
To expedite testing, Time-Dependent Dielectric Breakdown (TDDB) analyses are conducted on commercial 4H-SiC MOSFETs at high gate-to-source voltages (<inline-formula><tex-math notation="LaTeX">\bm ...{V_{GS}}</tex-math></inline-formula>), under Fowler-Nordheim conduction only. However, as inferred, such conditions induce impact ionization-generated holes in the dielectric layer (SiO<inline-formula><tex-math notation="LaTeX">\bm {_{2}}</tex-math></inline-formula>), resulting in a state transition in the effective dipolar moment. This accelerates the SiO<inline-formula><tex-math notation="LaTeX">\bm {_{2}}</tex-math></inline-formula> degradation leading to an overestimation of its intrinsic lifetime at typical <inline-formula><tex-math notation="LaTeX">V_{GS}</tex-math></inline-formula> values for gate driving in power converters. To address this, a physics-based approach is proposed to design TDDB tests under such conditions and to correct the intrinsic lifetime prediction at nominal <inline-formula><tex-math notation="LaTeX">\bm {V_{GS}}</tex-math></inline-formula> values, shortening the testing time by up to 2 orders of magnitude. Thus, the proposed method is a well-suited candidate to be considered in SiC power device qualification standards, still under development.
Humidity sensitivity of large area silicon sensors: Study and implications Fernández-Tejero, J.; Allport, P. P.; Aviñó, O. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2020, Volume:
978, Issue:
C
Journal Article
Peer reviewed
Open access
The production of large area sensors is one of the main challenges that the ATLAS collaboration faces for the new Inner-Tracker full-silicon detector. During the prototype fabrication phase for the ...High Luminosity Large Hadron Collider upgrade, several ATLAS institutes observed indications of humidity sensitivity of large area sensors, even at relative humidities well below the dew point. Specifically, prototype Barrel and End-Cap silicon strip sensors fabricated in 6-inch wafers manifest a prompt decrease of the breakdown voltage when operating under high relative humidity, adversely affecting the performance of the sensors. In addition to the investigation of these prototype sensors, a specific fabrication batch with special passivation is also studied, allowing for a deeper understanding of the responsible mechanisms. Here we present an extensive study of this behaviour on large area sensors. The locations of the hotspots at the breakdown voltage at high humidity are revealed using different infrared thermography techniques. Several palliative treatments are attempted, proving the influence of sensor cleaning methods, as well as baking, on the device performance, but no improvement on the humidity sensitivity was achieved. Furthermore, a study of the incidence of the sensitivity in different batches is also presented, introducing a hypothesis of the origins of the humidity sensitivity associated to the sensor edge design, together with passivation thickness and conformity. Several actions to be taken during sensor production and assembly are extracted from this study, in order to minimize the impact of humidity sensitivity on the performance of large area silicon sensors for High Energy Physics experiments.
Die-level current crowding phenomena are analyzed at the microsecond timescale with an internal IR-Laser Deflection set-up. To this end, the 4H-SiC plasma-optical coefficient for the refractive index ...is reported for the first time. A SiC Schottky diode with an edge termination based on a junction termination extension is used as a test vehicle. Under biasing conditions, the edge termination starts a local bipolar conduction along the device active area perimeter, leading to current crowding effects. Using refractive index measurements, a depth-resolved carrier profile is extracted and assessed using both, simulation and Free Carrier Absorption measurements.
For the first time, die-level current crowding phenomena are analyzed at the microsecond timescale with an internal IR-Laser Deflection (IIR-LD) set-up. As a test vehicle, a 1.2 kVSiC Schottky diode ...(1.6\times 1.6\mathrm{m}\mathrm{m}^{2} active area) with an edge termination based on a junction termination extension has been studied under 100 \mu \mathrm{s}-pulsed currents (ranging from 215 to 330 \mathrm{A}/\mathrm{c}\mathrm{m}^{2}). Under such conditions, the edge termination starts a local bipolar conduction along the device active area perimeter, leading to current crowding effects. To monitor this, an area on the lateral side-wall of 200\times 10\mu \mathrm{m}^{2} has been scanned in steps of 20 \mu \mathrm{m} through x-direction and 2 \mu \mathrm{m} along y-direction, thus obtaining 2D depth-resolved measurements.
Diamond is one of the best wide band-gap semiconductor materials available for high power devices development in terms of high current capability, high temperature operability, breakdown voltage and ...switching speed. Unfortunately, fabrication technology for diamond devices is still experimental and immature. Furthermore, one of the most critical fields to be addressed for practical diamond devices implementation concerns the development of power packaging solutions, given that limitations in the device packaging would hinder the performance of the device and act as the limiting factor for a technology that is still in a development state. Of special interest are the induced stresses and deformations caused by the thermo-mechanical mismatch between materials. These stresses and strains will be considerably different than the ones obtained with silicon or SiC dies, and it will be especially noticeable in high temperature applications due to the higher temperature swings and the reliability constraints that arise from the coefficient of thermal expansion mismatch and stiffness difference. In this paper, a Finite Element Method for thermo-mechanical simulation of a high-temperature thermal cycle for a full-stacked diamond die SOT-227 power module is introduced and compared to silicon- and SiC-die modules. Special interest is addressed to the analysis of stress and deformations generated in the die and die-attach solder layer.
In this work, SiC Schottky diodes specifically developed for the BepiColombo space mission are studied by Lock-in Infrared Thermography (LIT) to analyse local defects observed in their top ...metallization and passivation layers appeared after thermal vacuum tests. Such defects might potentially be the root cause of the increase in reverse leakage current measured after such accelerated tests.
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