Andrzej Kociubiński

Technology and characterization of 4H-SiC p-i-n junctions

Silicon Carbide (SiC) photodiodes have been proposed in recent years for ultraviolet (UV) light detection because of their robustness even in harsh environments, high quantum efficiency in all the UV range (200nm-400nm), excellent visible and infra-red blindness excluding UV filters implementation, low dark current and high speed. 4H-SiC has a bandgap three times larger (3.26eV) than Si and, thus, SiC detectors should have much higher sensitivity than Si detectors. In this paper, we present an overview of results on 4H-SiC p-i-n junctions fabrication and characterization. We used implantation technique to obtain p-region of the investigated structure. The ohmic contacts were formed using evaporation, etching and lift-off. Current-voltage, contact resistance and electroluminescence are the main characteristics of the presented devices. All the diodes showed excellent rectification with leakage current density of less than 10-9A/cm2.

Automatic detection of characteristic points and form of optical signals in multiparametric capillary sensors

The time series sequence of data readings are the input for computer aided analysis of signal from the multiparametric optical capillary sensor. The time series signals have characteristic points and forms. Their analysis by trained human operators is time consuming and sometimes lacks of precision because of the presence of signal noise. The noises can be mostly rejected with advanced electronic signal processing, but the output analog signal is often modified by the electromagnetic environment and by the noise generated by electronic elements. We propose and analyze an algorithm that can be used as an automatic detector of characteristic points and form of the time series signals that are produced by the measuring head and the analog electronic units of the biodiesel fuel quality test sensor.

Large-area transparent in visible range silicon carbide photodiode

This paper describes the construction, fabrication and properties of large-area ultra violet detector that is transparent in the visible range. The device was made on n-type 4H SiC substrate with a double epitaxial layer in which aluminum was implanted to form a p-n junction close to the surface, and a SiO2 layer was formed for passivation, without a guard ring. The design of the top and bottom electrodes of 4mm diameter UV sensitive area allows not less than 20% visible range transmission. This transmission was measured across sensitive area of examined devices and was only 5% lower than that of the substrate before implantation and electrodes deposition.

Innovative SiC over Si photodiode based dual-band, 3D integrated detector

This paper describes the fabrication of 3D-stacked, dual-band sensitive device and their preliminary characterization results. The device consists of two 3D integrated detectors. The square chip with fabricated 4H-SiC p-i-n junction was mounted on commercial silicon chip with large area VIS-photodiode made by Institute of Electron Technology in Warsaw. The UV-photodetector was made on n-type 4H-SiC substrate with a double epitaxial layer in which aluminum was implanted to form a p-n junction close to the surface, and a silicon dioxide layer was formed for passivation, without a guard ring. The optical and electrical characterization of each of the photodiode structures has been discussed including dark current and spectral response measurements of large-area silicon diode with 4H-SiC p-i-n junction. All the diodes showed excellent rectification with low leakage current.

Fabrication and characterization of epitaxial 4H-SiC pn junctions

This paper provides an overview of the process of 4H-SiC pn junction fabrication and characterization. The samples used in this study were fabricated in a resistively heated horizontal hot-wall Chemical Vapor Deposition reactor. The homo-epitaxial layers were grown on commercially available 4H-SiC substrates (Cree). In order to obtain p-type epilayers, they were intentionally doped with aluminum. In this work, we present our recently developed 4H-SiC pn junctions fabrication and characterization results. The ohmic contacts were formed using evaporation, etching, lift-off and high temperature annealing. Current-voltage characteristics of the devices were demonstrated.

4H-SiC photodiode model for DC SPICE circuit simulation

Technology, characterization and in particularly modeling of 4H-SiC photodiode have been presented in this paper. Modeling and simulation has been performed using PSPICE environment. Comparison of simulation with real results for electrical characteristic (I-V) of circular SiC photodiodes has been also presented.

Local liquid sample heating: integration and isolation of a micro-heater

Local liquid sample heating is used in multiparametric sensors of liquid type classification and in sensors of liquid flow. In such applications, the heating of the liquid is done by micro-heaters, with the liquid separated from the micro-heater. The presented paper concentrates on the physical conditions of liquid sample heating used in capillary sensors. In such devices the repeatable transfer of heat is required. The basic measurements include time of liquid to vapor phase transitions and local transfer of heat. In the work were used experimental and simulation techniques. The obtained results show that in the capillary sensor repeatable local heat transfer conditions can be easier achieved than repeatable time of liquid to vapor phase transitions. In the analyzed case, the local heating depends mostly on the capillary to micro-heater distance. The liquid to vapor transition times, beside of the liquid type, depend on the powers used for micro-heater heating and on capillary cross-section parameters, such as the inner and outer diameter values. By increasing the power to the micro-heater the transition time variability is reduced.

Design, modeling, and simulation of MEMS pressure sensors

This paper focuses on the design and analysis of a MEMS piezoresistive pressure sensor. The absolute pressure sensor with a 150μm wide and 3μm thick silicon membrane is modeled and simulated using CoventorWare™ softwareprofiting from a finite element method (FEM) implemented to determine specific electro-mechanical parameter values characterizing MEMS structure being designed. Optimization of piezoresistor parameters has been also performed to determine optimum dimensions of piezoresistors and their location referred to the center on the pressure sensor diaphragm. The output voltage measured on a piezoresistive Wheatstone bridge has been obtained and compared for two different resistor materials along with and linearity error analysis.

Multiparametric capillary sensor: stabilization of local heating

To this day, the micro-heating unit in a multiparametric capillary sensor’s setup has been controlled using laboratory power supply with constant voltage. In this method it was assumed that the micro heater’s resistance value is semi-constant. However, due to the fact that degradation effects induced by high power density dissipation in multiple, intense or prolonged heating cycles may cause it to vary, a new approach had to be found. Therefore, in this paper, a development of a power stabilization method using PID controller to compensate for micro-heater’s resistance changes during intense heating is described. Additionally, a current sensing resistor, a programmable power supply and a data acquisition system are incorporated into the setup to provide closed-loop feedback.

Modeling and simulation of nichrome microheater on polycarbonate substrate

This paper presents the design and simulation of four different structures of nichrome microheater on the polycarbonate substrate. Nichrome layer is covered by the silicon nitride dielectric layer. The comb capacitor covering dielectric layer is used for measuring electrical parameters of liquids. Designed structure allows impedance, resistance and capacitance monitoring of studied substances like chemical or biological liquids, which require constant heating value on the substrate surface. 3D model design and electro-thermal finite elements simulations were carried out by CoventorWare software. Various shapes of the heaters were studied to check the uniformity heating on the active surface.