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• 1.
KTH, School of Information and Communication Technology (ICT), Electronics.
KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics.
Low temperature Ni-Al ohmic contacts to p-TYPE 4H-SiC using semi-salicide processing2018In: International Conference on Silicon Carbide and Related Materials, ICSCRM 2017, Trans Tech Publications, 2018, Vol. 924, p. 389-392Conference paper (Refereed)

Most semiconductor devices require low-resistance ohmic contact to p-type doped regions. In this work, we present a semi-salicide process that forms low-resistance contacts (~10-4 Ω cm2) to epitaxially grown p-type (&gt;5×1018 cm-3) 4H-SiC at temperatures as low as 600 °C using rapid thermal processing (RTP). The first step is to self-align the nickel silicide (Ni2Si) at 600 °C. The second step is to deposit aluminium on top of the silicide, pattern it and then perform a second annealing step in the range 500 °C to 700 °C.

• 2.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
Silicon Carbide High Temperature Photodetectors and Image Sensor2019Doctoral thesis, comprehensive summary (Other academic)

Silicon Carbide (SiC) has the advantages of ultraviolet (UV) sensing and high temperature characteristics because of its wide band gap. Both merits make SiC photodetectors very attractive in astronomy, oil drilling, combustion detection, biology and medical applications. Driven by the objective of probing the high temperature surface of Venus (460 °C), this thesis develops SiC photodetectors and an image sensor for extremely high temperature functions. The devices and circuits are demonstrated through the procedure of layout design, in-house processing and characterizations on two batches.

The process flow has been optimized to be suitable for large scale integration (LSI) of SiC bipolar integrated circuits (IC). The improved processing steps are SiC dry etching, ohmic contacts and two-level metal interconnect with chemical-mechanical polishing (CMP). The optimized process flow is applied in the fabrication of discrete devices, a transistor-transistor logic (TTL) process design kit (PDK) and LSI circuits.

The photodetectors developed in this thesis, including photodiodes with various mesa areas, a phototransistor and a phototransistor Darlington pair have stable characteristics in a wide temperature range (25 °C ~ 500 °C). The maximum operational temperature of the p-i-n photodiode (550 °C) is the highest recorded temperature accomplished ever by a photodiode. The optical responsivity of the photodetectors covers the spectrum from 220 nm to 380 nm, which is UV-only.

The SiC pixel sensor and image sensor developed in this thesis are pioneer works. The pixel sensor overcomes the challenge of monolithic integration of SiC photodiode and transistors by sharing the same epitaxial layers and topside contacts. The pixel sensor is characterized from 25 °C to 500 °C. The whole image sensor circuit has 256 (16 ×16) pixel sensors and one 8-bit counter together with two 4-to-16 decoders for row/column selection. The digital circuits are built by the standard logic gates selected from the TTL PDK. The image sensor has 1959 transistors in total. The function of the image sensor up to 400 °C is verified by taking basic photos of nonuniform UV illumination on the pixel sensor array.

This thesis makes an important attempt on the demonstration of SiC opto-electronic on-chip integration. The results lay a foundation on the development of future high temperature high resolution UV image sensors.

• 3.
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
4H-SiC PIN diode as high temperature multifunction sensor2017In: 11th European Conference on Silicon Carbide and Related Materials, ECSCRM 2016, Trans Tech Publications Ltd , 2017, p. 630-633Conference paper (Refereed)

An in-house fabricated 4H-SiC PIN diode that has both optical sensing and temperature sensing functions from room temperature (RT) to 550 ºC is presented. The two sensing functions can be simply converted from one to the other by switching the bias voltage on the diode. The optical responsivity of the diode at 365 nm is 31.8 mA/W at 550 ºC. The temperature sensitivity of the diode is 2.7 mV/ºC at the forward current of 1 μA.

• 4.
KTH, School of Information and Communication Technology (ICT), Electronics.
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics.
550 degrees C 4H-SiC p-i-n Photodiode Array With Two-Layer Metallization2016In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 37, no 12, p. 1594-1596Article in journal (Refereed)

The p-i-n ultraviolet (UV) photodiodes based on 4H-SiC have been fabricated and characterized from room temperature (RT) to 550 degrees C. Due to bandgap narrowing at higher temperatures, the photocurrent of the photodiode increases by 9 times at 365 nm and reduces by 2.6 times at 275 nm from RT to 550 degrees C. Moreover, a 4H-SiC p-i-n photodiode array has been fabricated. Each column and row of the array is separately connected by two-layer metallization.

• 5.
KTH, School of Electrical Engineering and Computer Science (EECS).
KTH, School of Electrical Engineering and Computer Science (EECS). KTH, School of Electrical Engineering and Computer Science (EECS). KTH, School of Electrical Engineering and Computer Science (EECS).
A 4H-SiC BJT as a Switch for On-Chip Integrated UV Photodiode2019In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 40, no 1, p. 51-54Article in journal (Refereed)

This letter presents the design, fabrication, and characterization of a 4H-SiC n-p-n bipolar junction transistor as a switch controlling an on-chip integrated p-i-n photodiode. The transistor and photodiode share the same epitaxial layers and topside contacts for each terminal. By connecting the collector of the transistor and the anode of the photodiode, the photo current from the photodiode is switched off at low base voltage (cutoff region of the transistor) and switched on at high base voltage (saturation region of the transistor). The transfer voltage of the circuit decreases as the ambient temperature increases (2 mV/degrees C). Both the on-state and off-state current of the circuit have a positive temperature coefficient and the on/off ratio is >80 at temperature ranged from 25 degrees C to 400 degrees C. It is proposed that the on/off ratio can be increased by similar to 1000 times by adding a light blocking layer on the transistor to reduce light induced off-state current in the circuit.

• 6.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
High Temperature High Current Gain IC Compatible 4H-SiC Phototransistor2019Conference paper (Refereed)

This paper presents our in-house fabricated 4H-SiC n-p-n phototransistors. The wafer mapping of the phototransistor on two wafers shows a mean maximum forward current gain (βFmax) of 100 at 25 ºC. The phototransistor with the highest βFmax of 113 has been characterized from room temperature to 500 ºC. The βFmax drops to 51 at 400 ºC and remains the same at 500 ºC. The photo current gain of the phototransistor is 3.9 at 25 ºC and increases to 14 at 500 ºC under the 365 nm UV light with the optical power of 0.31 mW. The processing of the phototransistor is same to our 4HSiC-based bipolar integrated circuits, so it is a promising candidate for 4H-SiC opto-electronics onchip integration.

• 7.
KTH, School of Information and Communication Technology (ICT), Electronics.
KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT), Electronics. KTH, School of Information and Communication Technology (ICT).
Scaling and modeling of high temperature 4H-SiC p-i-n photodiodes2018In: IEEE Journal of the Electron Devices Society, ISSN 2168-6734, Vol. 6, no 1, p. 139-145, article id 8240922Article in journal (Refereed)

4H-SiC p-i-n photodiodes with various mesa areas (40,000μm2, 2500μm2, 1600μm2, and 400μm2) have been fabricated. Both C-V and I-V characteristics of the photodiodes have been measured at room temperature, 200 °C, 400 °C, and 500 °C. The capacitance and photo current (at 365 nm) of the photodiodes are directly proportional to the area. However, the dark current density increases as the device is scaled down due to the perimeter surface recombination effect. The photo to dark current ratio at the full depletion voltage of the intrinsic layer (-2.7 V) of the photodiode at 500 °C decreases 7 times as the size of the photodiode scales down 100 times. The static and dynamic behavior of the photodiodes are modeled with SPICE parameters at the four temperatures.

• 8.
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
Scaling of 4H-SiC p-i-n photodiodes for high temperature applications2017In: 2017 75th Annual Device Research Conference (DRC), Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)

Ultraviolet (UV) detection is important in astronomy, combustion detections and medical analysis. Solid-state UV detectors based on wide band gap semiconductors, such as 4H-SiC, are widely studied because of their excellent electrical properties [1]. 4H-SiC based UV detectors are solar blind and can be applied in extremely high temperature environments [2]. However, the state-of-art 4H-SiC photodetectors still have large sizes (&gt;10000 μm2), which are not suitable to be integrated into high resolution UV photography sensors. To build a full-frame UV imaging sensor containing megapixels, photodiodes smaller than 20 μm by side are necessary. Here, we report the fabrication and characterization of 4H-SiC p-i-n photodiodes with mesa areas scaled from 40000 μm2 to 400 μm2. The relationships between the parameters and the areas of the photodiodes are discussed. The photodiodes are fully functional from room temperature (RT) to 500 °C.

• 9.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems.
A Silicon Carbide 256 Pixel UV Image Sensor Array Operating at 400 degrees C2020In: IEEE Journal of the Electron Devices Society, ISSN 2168-6734, Vol. 8, no 1, p. 116-121Article in journal (Refereed)

An image sensor based on wide band gap silicon carbide (SiC) has the merits of high temperature operation and ultraviolet (UV) detection. To realize a SiC-based image sensor the challenge of opto-electronic on-chip integration of SiC photodetectors and digital electronic circuits must be addressed. Here, we demonstrate a novel SiC image sensor based on our in-house bipolar technology. The sensing part has 256 ( $16\times 16$ ) pixels. The digital circuit part for row and column selection contains two 4-to-16 decoders and one 8-bit counter. The digital circuits are designed in transistor-transistor logic (TTL). The entire circuit has 1959 transistors. It is the first demonstration of SiC opto-electronic on-chip integration. The function of the image sensor up to 400 degrees C has been verified by taking photos of the spatial patterns masked from UV light. The image sensor would play a significant role in UV photography, which has important applications in astronomy, clinics, combustion detection and art.

• 10.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
Process Control and Optimization of 4H-SiC Semiconductor Devices and Circuits2019In: Proceedings of the 3rd Electron Devices Technology and Manufacturing, (EDTM) Conference 2019, IEEE, 2019Conference paper (Refereed)
• 11.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
Metreveli, Alexy
Ur Rashid, Arman
Mantooth, Alan
Zetterling, Carl-Mikael
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
555-Timer IC Operational at 500 °C2019In: Bipolar SiC 555-timer IC, High Temperature ICs, TTL Comparator, SiC Integrated CircuitsArticle in journal (Other academic)

This paper reports an industry standard monolithic 555-timer circuit designed and fabricated in the in-house silicon carbide (SiC) low-voltage bipolar technology. The paper demonstrates the 555-timer ICs characterization in both astable and monostable modes of operation, with a supply voltage of 15 V over the wide temperature range of 25 to 500°C. Nonmonotonictemperature dependence was observed for the 555-timer IC frequency, rise-time, fall-time, and power dissipation.

• 12.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems.
Towards Silicon Carbide VLSI Circuits for Extreme Environment Applications2019In: Electronics, ISSN 2079-9292, Vol. 8, no 5Article in journal (Refereed)

A Process Design Kit (PDK) has been developed to realize complex integrated circuits in Silicon Carbide (SiC) bipolar low-power technology. The PDK development process included basic device modeling, and design of gate library and parameterized cells. A transistor–transistor logic (TTL)-based PDK gate library design will also be discussed with delay, power, noise margin, and fan-out as main design criterion to tolerate the threshold voltage shift, beta (β) and collector current (IC) variation of SiC devices as temperature increases. The PDK-based complex digital ICsdesign flow based on layout, physical verification, and in-house fabrication process will also be demonstrated. Both combinational and sequential circuits have been designed, such as a 720-device ALU and a 520-device 4 bit counter. All the integrated circuits and devices are fully characterized up to 500 °C. The inverter and a D-type flip-flop (DFF) are characterized as benchmark standard cells. The proposed work is a key step towards SiC-based very large-scale integrated (VLSI) circuits implementation for high-temperature applications.

• 13.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits. KTH, School of Electrical Engineering and Computer Science (EECS). KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems, Integrated devices and circuits.
A 600 degrees C TTL-Based 11-Stage Ring Oscillator in Bipolar Silicon Carbide Technology2018In: IEEE Electron Device Letters, ISSN 0741-3106, E-ISSN 1558-0563, Vol. 39, no 10, p. 1540-1543Article in journal (Refereed)

Ring oscillators (ROs) are used to study the high-temperature characteristics of an in-house silicon carbide (SiC) technology. Design and successful operation of the in-house-fabricated 4H-SiC n-p-n bipolar transistors and TTL inverter-based 11-stage RO are reported from 25 degrees C to 600 degrees C. Non-monotonous temperature dependence was observed for the oscillator frequency; in the range of 25 degrees C to 300 degrees C, it increased with the temperature (1.33 MHz at 300 degrees C and V-CC = 15 V), while it decreased in the range of 300 degrees C-600 degrees C. The oscillator output frequency and delay were also characterized over a wide range of supply voltage (10 to 20 V). The noise margins of the TTL inverter were also measured; noise margin low (NML) decreases with the temperature, whereas noise margin high (NMH) increases with the temperature. The measured power-delay product (P-D . T-P) of the TTL inverter and 11-stage RO was approximate to 4.5 and approximate to 285 nJ, respectively, at V-CC= 15 V. Reliability testing indicated that the RO frequency of oscillation decreased 16% after HT characterization.

• 14.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. Univ Arkansas, Dept Elect Engn, Fayetteville, AR 72701 USA.. Univ Arkansas, Dept Elect Engn, Fayetteville, AR 72701 USA.. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
555-Timer and Comparators Operational at 500 degrees C2019In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 66, no 9, p. 3734-3739Article in journal (Refereed)

This paper reports an industry standard monolithic 555-timer circuit designed and fabricated in the in-house silicon carbide (SiC) low-voltage bipolar technology. This paper demonstrates the 555-timer integrated circuits (ICs) characterization in both astable and monostable modes of operation, with a supply voltage of 15 V over the wide temperature range of 25 degrees C-500 degrees C. Nonmonotonic temperature dependence was observed for the 555-timer IC frequency, rise time, fall-time, and power dissipation.

• 15.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits. KTH.
KTH, School of Electrical Engineering and Computer Science (EECS), Electronics. KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
A Monolithic 500 °C D-flip flop Realized in Bipolar 4H-SiC TTL technology2019Conference paper (Other academic)
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