Hybrid Layered Nanosystems Using Ferromagnetic and Piezoelectric Materials for Magnetic Memory Applications (Hybride gelaagde systemen gebaseerd op ferromagnetische en piëzo-elektrische materialen voor magnetische geheugentoepassingen)

Acknowledgements i Nederlandse samenvatting iii Abstract v Acronyms vii List of Symbols ix Contents xi Chapter 1 Introduction 1 Chapter 2 Theoretical background 9 2.1 Introduction 9 2.2 Elasticity 9 2.2.1 Stress 10 2.2.2 Strain 12 2.2.3 Young's modulus 14 2.2.4 Poisson’s ratio 14 2.3 Piezoelectricity 15 2.3.1 Origin of piezoelectricity 15 2.3.2 Piezoelectric coefficients and constants 19 2.3.3 Polarization 22 2.3.4 Piezoelectric materials 24 2.3.5 Ferroelectric hysteresis 27 2.4 Ferromagnetism 29 2.4.1 Origin of ferromagnetism 29 2.4.2 Magnetic domains 29 2.4.3 Magnetic hysteresis 30 2.5 Magnetoelasticity 31 2.5.1 Magnetostriction 31 2.5.2 Villari effect or inverse magnetostriction 35 2.5.3 ΔE effect 36 2.5.4 Magnetostrictive materials 37 2.6 Surface acoustic waves 39 2.6.1 Historical overview 39 2.6.2 The interdigital transducer 41 2.6.3 Saw piezoelectric substrates 43 2.7 Characterization techniques 45 2.7.1 Magnetoresistive techniques 45 2.7.2 Magneto-Optic Kerr Effect (MOKE) 50 2.7.3 Alternating Gradient Force Magnetometer (AGFM)51 2.7.4 Pushing Machine (PUMA) system 52 Chapter 3 Voltage assisted magnetic switching 59 3.1 Introduction 59 3.2 Experimental results 60 3.2.1 Electric field controlled hysteresis curves in magnetostrictive single thin films 63 3.2.2 Electric field controlled hysteresis curves in spin valves 69 3.2.3 Electrical switching without external magnetic fields 71 3.2.4 Magnetically assisted electrical switching 72 3.2.5 Scaling down for components 74 3.2.6 Alternative magnetostrictive material 75 3.3 Discussion 77 3.4 Conclusion 78 Chapter 4 Magnetic tuning of surface acoustic wave (SAW) devices 81 4.1 Introduction 81 4.2 SAW device fabrication 82 4.3 Magnetic tuning of the phase of SAW devices 86 4.3.1 Tuning results 89 4.4 Magnetic tuning of the centre operation frequency of SAW devices 105 4.5 Results and discussion 112 4.6 Conclusion 114 Chapter 5 Magnetic ferroelectric coupling in the resonant regime 117 5.1 Introduction 117 5.2 Fundamentals of ferromagnetic resonance 118 5.2.1 Magnetoelastic energy term 119 5.3 Experiments 121 5.3.1 Kittel formula 121 5.3.2 SAW device 122 5.3.3 Macrospin simulations 123 5.4 Results and discussion 125 5.5 Conclusion 127 Chapter 6 Summary and outlook 129 6.1 Summary 129 6.2 Outlook 131 Curriculum Vitae 133 Scientific contributions 135nrpages: 152status: publishe

Live Demonstration: Front and Back Illuminated Dynamic and Active Pixel Vision Sensor Comparison

The demonstration shows the differences between two novel Dynamic and Active Pixel Vision Sensors (DAVIS). While both sensors are based on the same circuits and have the same resolution (346×260), they differ in their manufacturing. The first sensor is a DAVIS with standard Front Side Illuminated (FSI) technology and the second sensor is the first Back Side Illuminated (BSI) DAVIS sensor

In-vivo imaging of neural activity with dynamic vision sensors

Optical recording of neural activity using calcium or voltage indicators requires cameras capable of detecting small temporal contrast in light intensity with sample rates of 10 Hz to 1 kHz. Large pixel scientific CMOS image sensors (sCMOS) are typically used due to their high resolution, high frame rate, and low noise. However, using such sensors for long-term recording is challenging due to their high data rates of up to 1 Gb/s. Here we studied the use of dynamic vision sensor (DVS) event cameras for neural recording. DVS have high dynamic range and a sparse asynchronous output consisting of brightness change events. Using DVS for neural recording could avoid transferring and storing redundant information. We compared the use of a Hamamatsu Orca V2 sCMOS with two advanced DVS sensors (a higher temporal contrast sensitivity 188×180 pixel SDAVIS and a 346×260 pixel higher light sensitivity back-side-illuminated BSIDAVIS) for neural activity recordings with fluorescent calcium indicators both in brain slices and awake mice. The DVS activity responds to the fast dynamics of neural activity, indicating that a sensor combining SDAVIS and BSIDAVIS technologies would be beneficial for long-term in-vivo neural recording using calcium indicators as well as potentially faster voltage indicators

Front and Back Illuminated Dynamic and Active Pixel Vision Sensor Comparison

Back side illumination has become standard image sensor technology owing to its superior quantum efficiency and fill factor. A direct comparison of front and back side illumination (FSI and BSI) used in event-based dynamic and active pixel vision sensors (DAVIS) is interesting because of the potential of BSI to greatly increase the small 20% fill factor of these complex pixels. This brief compares identically designed front and back illuminated DAVIS silicon retina vision sensors. They are compared in term of quantum efficiency (QE), leak activity and modulation transfer function (MTF). The BSI DAVIS achieves a peak QE of 93% compared with the FSI DAVIS, peak QE of 24%, but reduced MTF, due to pixel crosstalk and parasitic photocurrent. Significant “leak events” in the BSI DAVIS limit its use to controlled illumination scenarios without very bright light sources. Effects of parasitic photocurrent and modulation transfer functions with and without IR cut filters are also reported

Telling Stories with a Synthetic Character: Understanding Inter-modalities Relations

Abstract. Can we create virtual storytellers that have enough expressive power to convey a story? This paper presents a study comparing the storytelling ability between a virtual and a human storyteller. In order to evaluate it, three means of communication were taken into account: voice, facial expression and gestures. One hundred and eight students from computer engineering watched a video where a storyteller narrated the traditional Portuguese story entitled ”O Coelhinho Branco ” (The little white rabbit). The students were divided into four groups. Each of these groups saw one video where the storyteller was portrayed either by a synthetic character or a human. The storyteller’s voice, no matter the nature of the character, could also be real or synthetic. After the video display, the participants filled a questionnaire where they rated the storyteller performance. As expected the synthetic versions used in the experiment obtained lower classifications than their natural counterparts. The data suggests that the gap between synthetic and real gestures is the smallest while the synthetic voice is the furthest from its natural version. An interesting result was that the classification of the facial expression is affected by the nature of the voice.

Thin-film photodetectors for NIR and SWIR Image Sensors with 0.13 μm tech node CMOS read-out

status: Published onlin

NIR sensors based on photolithographically patterned PbS QD photodiodes for CMOS integration

status: Published onlin

NIR sensors based on photolithographically patterned PbS QD photodiodes for CMOS integration

The integration of infrared sensitive thin-film materials with solution processing capabilities on top of Si substrates is a significant step towards cost-efficient infrared imagers. Colloidal quantum dots based on lead sulfide are very attractive materials for the realization of novel image sensors combining low cost synthesis and processing with deposition over large area and on any substrate. The tunable band gap enables selective detection in wavelengths ranging from the visible up to the short-wave-infrared (SWIR). This work describes the first results of a roadmap that will enable the integration of quantum dot photodiodes (QDPD) on top of a Si based CMOS read-out circuit. Photodiodes using an n-p junction architecture are fabricated on Si substrates, showing low dark current of 30 nA/cm(2) at -1 V reverse bias, EQE above 20% and specific detectivity higher than 10(12) cm Hz(1/2) W-1 at the wavelength of 940 nm. Efficiency is improved by tuning the top contact transparency with optical modeling. Furthermore, photolithographic patterning of the thin-film stack is introduced for the first time, showing the feasibility of pixel pitches down to 40 mu m, opening the way towards high resolution monolithic infrared imagers and the incorporation of infrared sensitive pixels next to visible ones