Mikroteknologi och nanovetenskap (MC2) // Microtechnology and Nanoscience (MC2)
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Kombinerar fundamental och tillämpad forskning med fokus på framtidens elektronik, fotonik, bio- och nanosystem, och har en unik forskarmiljö med sina mät- och renrumsfaciliteter.
Institutionen för mikroteknologi och nanovetenskap, till vardags förkortat MC2, bedriver unik forskning inom mikro- och nanoteknologi och består av fler än 200 forskare och forskarstuderande. Vår forskning är inriktad mot framtidens nano- och kvantmekaniska elektronik, fotonik, bio- och nanosystem.
För forskning och forskningspublikationer, se https://research.chalmers.se/organisation/mikroteknologi-och-nanovetenskap-mc2/
Conducts basic and applied research into future electronics, photonics, bio and nano systems. Cleanroom facilities ensure a unique research environment.
The Department of Microtechnology and Nanoscience – MC2 – is a unique research department in the areas of micro- and nanotechnology, housing more than 200 researchers and PhD students. We focus our research on the areas of future nano- and quantum electronics, photonics, bio- and nano systems.
Studying at the Department of Microtechnology and Nanoscience at Chalmers
For research and research output, please visit https://research.chalmers.se/en/organization/microtechnology-and-nanoscience-mc2/
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Browsar Mikroteknologi och nanovetenskap (MC2) // Microtechnology and Nanoscience (MC2) efter Program "Applied physics (MPAPP), MSc"
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- PostCharacterisation of high-frequency noise in graphene FETs at different ambient temperatures(2019) Li, Junjie; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Stake, Jan; Yang, XinxinGraphene is a promising channel material for high-frequency field-effect transistors, owing to its intrinsically high carrier velocity and purely two-dimensional structure. At high frequencies, the noise originated in device itself, especially the thermal noise, becomes very crucial for the performance of transistors. The thermal noise can be influenced by ambient temperature or self-heating due to high drain bias. This motivates the study of the effect of temperature on the noise performance of graphene field-effect transistors (GFETs). In this thesis, the results on high-frequency noise characterisation and modelling of the GFETs at different temperature and bias conditions are presented. The basic idea and main procedures of high-frequency noise modelling are based on Pospieszalski’s noise model. Two different high-frequency noise characterisation techniques, i.e., the Y-factor and cold-source methods, and two calculation methods of highfrequency noise parameters, i.e., the source-pull and 50 ohm impedance termination (F50) methods, have been analysed and discussed. The high-frequency noise of the GFETs at an ambient temperature range from -60 C to 25 C is presented. The minimum noise figure (Fmin) of the GFETs decreases with the drain bias and saturates above approximately -1 V due to the carrier mobility saturation in the channel. The noise performance shows a rather strong dependence on both temperature and gate bias mainly due to the change of carrier density and the contact resistance. The minimum noise figure (Fmin) is 1.2 dB at 6.5 GHz at room temperature, which is comparable with that of the best metal-semiconductor field effect transistors. And it decreases down to 0.3 dB at 8 GHz for an ambient temperature of -60 C. An empirical noise model for the GFETs considering both temperature and gate voltage has been proposed and verified by the experimental results. In conclusion, a way to characterise the temperature dependence of noise performance of the GFETs is discussed, which allows for further development of low-noise GFETs for high-frequency applications.
- PostDesign of nanowire-based vertical-cavity surface-emitting lasers(2018) Bengths, Marcus; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceThe optical losses have been studied in a novel nanowire-based GaN vertical-cavity surface-emitting laser as a function of different design parameters. The simulations were based upon the finite element frequency domain method and were implemented in COMSOL Multiphysics® simulation software. The results show that the threshold material gain depends most strongly on the platelet radius. Lasers with a small platelet radii are shown to suffer from large and inevitable diffraction losses. Hence, in order to reach decent threshold material gain and achieve lasing with the current geometric design, the platelet radius must be increased to at least 1200nm to 1300nm. Additional diffraction losses derive from the pitched top of the platelet, but these can be suppressed by depositing a concave top distributed Bragg reflector (DBR) with focusing abilities. The threshold material gain can be further reduced by some extent by adding additional mirror pairs in the top DBR. Furthermore, the thickness and materials of the cladding layer also strongly affects the threshold material gain. However, the influence of the cladding layer is clearly different between having a flat top DBR or a concave top DBR. This complex influence of the cladding layer requires further investigation. The method presented has been proven robust, and comparable results to a beam propagation method (BPM) validates its accuracy. Being far less computationally heavy than BPM, it will be an important tool in the future design of novel lasers.
- PostElectrical Conductivity of n-doped GaN-based Distributed Bragg Reflectors(2016) Hjort, Filip; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceVertical-cavity surface-emitting lasers (VCSELs) could find new applications in areas ranging from displays to bio-medicine if their wavelengths were extended into the blue spectrum. However, the realization of GaN-based VCSELs have proven to be challenging. One of the major hurdles have been to achieve epitaxially grown distributed Bragg reflectors (DBRs) with high reflectivity and vertical electrical conductivity. A vertically conductive DBR would allow the n-contact to be moved outside the cavity, reducing the cavity length and leading to significantly improved laser performance for blue-emitting GaN-based VCSELs. To electrically characterize a DBR, low-temperature annealed ohmic contacts to n-doped GaN are essential, since the DBRs often have built-in-strain and thus could crack when exposed to temperature rampings. Ohmic contact formation of Al, Ta/Al/Ta, and Ti/Al/Ti/Au contacts on n-GaN with different concentrations doping was studied for annealing temperatures up to 700°C by transmission line measurements. On highly doped n-GaN (n = 2.5 × 10^19 cm−3) the Al contacts were ohmic as-deposited and had a minimum specific contact resistivity of 3 × 10−7 cm^2. Al contacts had the lowest contact resistivity reported for ohmic contacts on n-GaN annealed under 500°C. Ta/Al/Ta contacts had lowest resistivity for annealing over 500°C and were thermally stable up to at least 700°C. No ohmic contact to low-doped n-GaN (n < 3 × 10^17 cm−3) was found. The effect of interlayers on the vertical electrical conductivity of AlN/GaN DBRs was investigated by IV-measurements on four different 10.5 DBR pair samples (Sample A-D). Sample A had no interlayers, samples B and C had one pair of AlN/GaN interlayers with thicknesses of 2 nm/2 nm and 0.5 nm/0.5 nm at each interface, respectively, and sample D had graded interlayers from GaN to AlN over 1.5 nm thickness. The electrical conductivity of 8 and 9 DBR pairs was investigated by etching mesas to different etch depths and depositing Al-contacts on top and on the etched surface next to the mesa. The series resistance scaled with mesa area and the lateral and contact resistance contribution was less than 10% of the total resistance. Sample A had a mean specific series resistance of 0.043 cm^2 for 8 pairs, which is comparable to state-of-the-art for n-doped AlN/GaN DBRs. The mean specific series resistances for Sample B and D were 4 times higher than that of sample A, and 10 times higher for Sample C, indicating that interlayers used for strain compensation can increase the electrical resistivity of n-doped AlN/GaN DBRs. An MBE-grown n-doped ZnO/GaN DBR was characterized in a similar manner and showed a specific series resistance of less than 10−3 cm2 for 3 pairs. The lateral and contact resistance were dominating over the vertical resistance, which made an accurate determination of the DBR conductivity difficult. Ga-droplets, which covered the DBR surface, were ruled out as the reason for the low vertical resistance by investigating small droplet-free mesas. This is the first report on electrically conducting ZnO/GaN DBRs.
- PostHow Anode Porosity a ects the performance of a Solid Oxide Fuel Cell(2014) Billemar, Jakob; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceThe purpose of this project was to investigate how parameters, such as size of zirconia particles and the porosity, impact the performance of the anode of a solid oxide fuel cell. The analysis that has been conducted was focused on investigating SEM-pictures and analysing electrochemical impedance spec- troscopy(EIS) measurements on half-cells. The data suggest that an increasing porosity lead to an almost linear increase of TPBs/area in the range of 20- 40%. From the results, it was not obvious that the amount of triple phase boundaries(TPBs) was dependent on the size of the zirconia particles in the range between 0.12 and 1m. The EIS measurements suggest that the activation energy resulting from the first arc decreased as more measurements were done, at least for the sam- ple named Red. half-cell. This effect could be within the margin of errors, and hence just a coincidence. It could also be seen that the sample with the thickest electrolyte gave rise to the highest impedance, but not a much higher activation energy than the other reduced samples. Furthermore there appear to be a difference in shape between reduced and not reduced samples, and a substantial differences regarding activation energy and conductivity could also be seen.
- PostModelling of Digital Radar(2016) Jonasson Svärdsby, Albin; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceThe advances in modern electronics pave way for new ways to design radar systems. The existence of Analogue to Digital Converters (ADC) capable of sampling at GHz make it possible to sample the RF signal directly, removing the need for prior down mixing. This gives a possibility to design very simple receiver channels and move traditional operations from hardware to software. This greatly helps cutting cost of manufacturing and development and opens up for a very configurable system. This configurability comes at the cost of decreased selectivity, resulting in that external signals outside the radar system's signal bandwidth but inside the receiver band will become amplified as well, with the risk of saturating the amplifiers. Because of this it is interesting to study the impact of the non-linearities on detectability. The simple design of the system makes it feasible to simulate the full system chain from transmitter to signal processing after the receiver. This thesis treats the methods used to create a model in order to simulate the operation and non-linear effects of a Uniform Linear Array (ULA) digital pulse doppler radar system from generation of transmission waveform to the signal processing of the sampled output from the receiver channels. The methods involve electronic simulations of amplifiers utilising a 5th degree polynomial and filtering and sampling processes. The thesis further features techniques used to enhance the Signal to Noise Ratio (SNR) of a desired signal from a phased array and position it in a 3D space with 2 room dimensions and 1 velocity dimension. The model is then utilised to study the effects of non-linear effects of the system when the input to the receiver is disturbed by a strong clutter signal or a strong external signal. The thesis also treats the effect on detectability of a target when an external signal give rise to higher order harmonics from amplifier saturation and clipping during sampling that then is folded into the radar system's final sampling band. The thesis finds it feasible to perform full system simulations from waveform generation to detection and it is found that the non-linear effects due to strong disturbances negatively affect the desired target SNR and may in some cases be the source of false detections. The results is found by studying common radar cases, with varying input power to the receiver. The thesis finds that it is possible to digitally suppress external signals outside the final sampling band but the decrease in SNR for the desired signal, due to saturation of the radar system, still remains.
- PostThermal annealing of ZnO and Al2O3 substrates(2015) Hawrami, Banaz Muzaffar; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceZnO is a compound semiconductor with a wide and direct bandgap of 3.3 eV which corresponds to UV light. This makes ZnO suitable for the violet-blue emitting optoelectronic devices. However, there are several challenges to obtain these devices. The substrate surfaces needs to be very smooth for epitaxial growth. This thesis focuses on the morphology of the Zn- and O-faces of ZnO and Al2O3 surfaces before and after thermal annealing. Several annealing parameters have been varied and the samples are analyzed by AFM and XRD. It turns out that for a high annealing temperature, the surface of Zn-face was improved. Atomic steps could observed on the surface. Smooth O-face surfaces were achieved at relatively low annealing temperatures. Sapphire is also a possible substrate for ZnO, it has also been investigated in this thesis.
- PostTransmission Electron Microscope Specimen Preparation Techniques for Studies of Surface Plasmon Resonance Bio-sensing Detectors Based on Nanostructured TiO2 and Au Bilayer Films(2011) Esfahani, Maryamsadat Khoshouei; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceThis work concerns the microstructure of surface plasmon resonance bio sensing detectors that enable label-‐free detection of small amounts of proteins. The detectors are based on metal multilayer films with nano holes on glass substrates. As proteins bind to the holes small changes are induced in the dielectric, which can be probed using localized surface plasmon resonance (LSPR) spectroscopy. The response to different proteins depends on the fine scale microstructure of the detectors including the structure of the holes and the interfaces between the film layers in the metal and between metal and substrate. Electron energy loss spectroscopy (EELS) in the trans-mission electron microscope (TEM) can provide information about the correlation between plasmon response and the microstructure. The samples need to be thin, i.e. less than 100 nm, in order to be transparent to the electron beam. It is important to image and perform the spectro-scopy of the detector structures using both plan view and cross section specimens. The first type of specimens provides an overview of the sample and information about the fine scale morphology of the small holes. The second type reveals the structure of the different interfaces of the detector multilayers. The TEM specimens need to be representative of the original detectors. The details of the specimen preparation methods are crucial for obtaining high quality specimens suitable for the TEM studies. The preparation parameters depend on the geometry and materials of the detectors. This work concerns the develop-ment of specimen preparation techniques for the surface plasmon resonance bio-‐sensing detectors. Both plan view and cross section TEM specimens with good quality have been prepared and suitable parameters identified. It has also been shown that it is possible to prepare TEM specimens from regions with individual small holes using a combined focused ion beam (FIB)-‐ scanning electron microscope (SEM).