Impact of Memory Frequency Scaling on User-centric Smartphone Workloads

Improving battery life in mobile phones has become a top concern with the increase in memory and computing requirements of applications with tough quality-of-service needs. Many energy-efficient mobile solutions vary the CPU and GPU voltage/frequency to save power consumption. However, energy-aware control over the memory bus connecting the various on-chip subsystems has had much less interest. This measurement-based study first analyse the CPU, GPU and memory cost (i.e. product of utilisation and frequency) of user-centric smartphone workloads. The impact of memory frequency scaling on power consumption and quality-of-service is also measured. We also present a preliminary analysis into the frequency levels selected by the different default governors of the CPU/GPU/memory components.We show that an interdependency exists between the CPU and memory governors and that it may cause unnecessary increase in power consumption, due to interference with the CPU frequency governor. The observations made in this measurement-based study can also reveal some design insights to system designers

Characterization and Fatigue of the Converse Piezoelectric Effect in PZT Films for MEMS Applications

A measurement setup for the detailed study of the transverse piezoelectric coefficient e(31,f) in the converse (actuator) mode was developed. It allows the assessment of the piezoelectric stress in thin films on silicon cantilevers and provides for a correlation of this stress with large and small signal responses to ferroelectric polarization and dielectric response, both as a function of slowly sweeping electric field. This test is important for the understanding of piezoelectric thin films in microelectromechanical systems. The method is illustrated at hand of sol-gel lead-zirconate-titanate (PZT) thin films, and verified also with AlN and AlN-ScN alloy thin films. A 1-mu m thick, sol-gel derived PZT(53/47) gradient-free sample showed a response of -18.3 C/m(2) at 100-kV/cm electric field. Reliability tests of PZT thin films were carried out with the same setup in an accelerated manner. The piezoelectric activity did not degrade significantly up to 109 unipolar pulses at 100 kHz with an amplitude of -150 kV/cm. The increase in leakage toward the end of the cycles was explained by a thermal runaway effect

Piezoelectric AlScN thin films: A semiconductor compatible solution for mechanical energy harvesting and sensors

The transverse piezoelectric coefficient e31,f of Al1-xScxN thin films was investigated as a function of composition. It increased nearly 50% from x = 0 to x = 0.17. As the increase of the dielectric constant was only moderate, these films are very suitable for energy harvesting, giving a 60% higher transformation yield (x = 0.17) as compared to pure AlN. A higher doping might even lead to a 100% augmentation. The thickness strain response (d33,f) was found to increase proportionally to the ionic part of the dielectric constant. The e-type coefficients (stress response), however, did not augment so much as the structure becomes softer. As a result, the transverse voltage/strain response (h31,f-coefficient) was raised only slightly with Sc doping. The low dielectric loss obtained at all compositions suggests also the use of Al1xScxN thin films in sensors

Effect of excess surfactant on transport of surface-active model drugs and emulsion stability in triphasic systems

The overall objective of this research are to predict transport of model drugs in triphasic (oil, water and micellar) emulsion system using various physicochemical parameters and mathematical models and to determine the effect of surface—active model drugs on transport in triphasic emulsions and on emulsion stability. Excess surfactant is present in most emulsions in the form of monomers and micelles to aid the stability of these systems. Excess surfactant may alter the kinetics of drug release by: micellar solubilization, alteration of the drug partitioning process, and drug/surfactant complexation. Surface—active drugs may associate with the surfactant and may alter the interfacial area, emulsion stability and transport kinetics of the drugs across the emulsion interface. A range of model drugs with similar structures, different lipophilicities and different surface—activities were selected to investigate the influence of excess surfactant on model drug transport and emulsion stability in triphasic systems. Phenylazoaniline, Benzocaine, Phenobarbital and Barbital were investigated. Light mineral oil was chosen as the oil phase. An ionic surfactant, cetyltrimethylammonium bromide and a nonionic surfactant, polyoxyethylene (10) oleyl ether were chosen to determine the effect of the ionic nature of the surfactant on model drug transport and emulsion stability in triphasic systems. Model drug transport in the triphasic systems was investigated using side-by-side diffusion cells mounted with hydrophilic dialysis membranes (molecular weight cutoffs 1 KD and 50 KD) and bulk equilibrium reverse dialysis bag method. The bulk equilibrium reverse dialysis bag method involves infinite dilution of the emulsions in a continuous phase and the model drugs are released into suspended dialysis bags. Emulsion stability was determined by droplet size analysis as a function of time and temperature using photon correlation spectroscopy and a light blockage technique. Violation of sink conditions during the transport studies occurred using the side-by-side diffusion cell method. This limitation was overcome using the bulk equilibrium reverse dialysis bag technique. The transport rate of the model drugs in triphasic systems were affected by the ionic nature of the surfactants, model drug surface—activity and lipophilicity. Mathematical models were developed using Fick\u27s first law and consecutive rate equations. The models were predictive of the experimental data.

Advanced sol-gel processing of PZT thin films for piezoelectric MEMS structures

Micro-electro-mechanical systems (MEMS) technology is revolutionizing industrial and consumer products by replacing bulky devices by miniaturized versions that are suitable for portable applications as for instance in mobile phones. Besides small size, the keys for the success are reproducibility, batch processing, and significantly cheaper prices due to mass production. Whereas standardMEMS processing relied fromits beginning on standard CMOS materials, increasing need in extreme requirements or exploitation of specific phenomena demands for the integration of new materials. The interest is particularly strong in piezoelectric MEMS devices due to their higher efficiency in converting electrical to mechanical energy and vice versa, and thus their ability to provide electro-mechanical transducers. Since most of the actively used piezoelectric materials are ceramic in nature, they must be synthesized at rather high temperatures, which pose challenges to integration routes. The recent years can be considered as the starting phase of product development of piezo-MEMS. As a result, a very high interest is put on further improving the quality of piezoelectric thin films, meaning higher sensitivity in MEMS sensors and larger stroke inmicro-actuators is remaining a key priority. Themost widely used piezoelectric thin filmmaterials forMEMS devices are zinc oxide (ZnO), aluminumnitride (AlN) and lead zirconate titanate (PZT). AlN is used extensively forMEMS resonator structures due to its high quality factor and low losses. It is also investigated for sensors where linearity and stability of the piezoelectric response is mandatory. PZT films are used in actuators and acoustic transducer applications because of their high piezoelectric coefficients and electromechanical coupling coefficients. In this work, energy harvesting is specifically considered as motivation for property evaluation and optimization. In this case, the piezoelectric thin filmis used like a sensor for vibrations andmotions, though with the optimization requirement that the product of current and voltage must be maximal. [...

Comparison of lead zirconate titanate (PZT) thin films for MEMS energy harvester with interdigitated and parallel plate electrodes

PZT thin films on insulator buffered silicon substrates with interdigitated electrodes (IDEs) have the potential to harvest more energy than parallel plate electrode (PPE) structures, because IDE structures exploit the longitudinal piezoelectric effect, which is about twice as high as the transverse piezoelectric effect exploited with PPE structures. There are only few studies on PZT IDE structures and their piezoelectric properties, and even no studies with a direct experimental comparison of the two options. The biggest challenge in using PZT with IDE structures are texture control on insulating buffer layers, and efficient poling at higher electrode gaps. Still, IDE structures are better suited for energy harvesting application as they can generate higher voltages with the same strain. We have proposed a figure of merit (FOM) for easy comparison with similar parallel plate electrode (PPE) structures. Our FOM corresponds to twice the energy density stored per unit strain deformation. For 1 mu m random PZT on titania buffered silicon, a FOM of 1.26 x 10(10) J/m(3) and 12.9 mV/mu strain was achieved when compared to 1.03 x 10(10) J/m(3) and 1.14 mV/mu strain for highly oriented, well poled 1 mu m PZT with PPE system

Measurement of effective piezoelectric coefficients of PZT thin films for energy harvesting application with interdigitated electrodes

Interdigitated electrode (IDE) systems with lead zirconate titanate (PZT) thin films play an increasingly important role for two reasons: first, such a configuration generates higher voltages than parallel plate capacitor-type electrode (PPE) structures, and second, the application of an electric field leads to a compressive stress component in addition to the overall stress state, unlike a PPE structure, which results in tensile stress component. Because ceramics tend to crack at relatively moderate tensile stresses, this means that IDEs have a lower risk of cracking than PPEs. For these reasons, IDE systems are ideal for energy harvesting of vibration energy, and for actuators. Systematic investigations of PZT films with IDE systems have not yet been undertaken. In this work, we present results on the evaluation of the in-plane piezoelectric coefficients with IDE systems. Additionally, we also propose a simple and measurable figure of merit (FOM) to analyze and evaluate the relevant piezoelectric parameter for harvesting efficiency without the need to fabricate the energy harvesting device. Idealized effective coefficients e(IDE) and h(IDE) are derived, showing its composite nature with about one-third contribution of the transverse effect, and about two-thirds contribution of the longitudinal effect in the case of a PZT film deposited on a (100)-oriented silicon wafer with the in-plane electric field along one of the Si directions. Randomly oriented 1-mu m-thick PZT 53/47 film deposited by a sol-gel technique, was evaluated and yielded an effective coefficient e(IDE) of 15 C.m(-2). Our FOM is the product between effective e and h coefficient representing twice the electrical energy density stored in the piezoelectric film per unit strain deformation (both for IDE and PPE systems). Assuming homogeneous fields between the fingers, and neglecting the contribution from below the electrode fingers, the FOM for IDE structures with larger electrode gap is derived to be twice as large as for PPE structures, for PZT-5H properties. The experiments yielded an FOM of the IDE structures of 1.25 x 10(10) J/m(3) and 14 mV/mu strain

Comparison of Lead Zirconate Titanate Thin Films for Microelectromechanical Energy Harvester With Interdigitated and Parallel Plate Electrodes

Lead zirconate titanate (PZT) thin films on insulator-buffered silicon substrates with interdigitated electrodes (IDEs) have the potential to harvest more energy than parallel plate electrode (PPE) structures because the former exploit the longitudinal piezoelectric effect, which is about twice as high as the transverse piezoelectric effect used by PPE structures. In this work, both options are compared with respect to dielectric, ferroelectric, and piezoelectric properties, leakage currents, and figure of merit (FOM) for energy harvesting. The test samples were silicon beams with {100} PZT thin films in the case of the PPE geometry, and random PZT thin films for the IDE geometry. Both films were obtained by an identical sol-gel route. Almost the same dielectric constants were derived when the conformal mapping method was applied for the IDE capacitor to correct for the IDE geometry. The dielectric loss was smaller in the IDE case. The ferroelectric loops showed a higher saturation polarization, a higher coercive field, and less back-switching for the IDE case. The leakage current density of the IDE structure was measured to be about 4 orders of magnitude lower than that of the PPE structure. The best FOM of the IDE structures was 20% superior to that of the PPE structures while also having a voltage response that was ten times higher (12.9 mV/mu strain)