Bulk micromachining of silicon in TMAH-based etchants for aluminum passivation and smooth surface

The fabrication of silicon based micromechanical sensors often requires bulk silicon etching after aluminum metallization. All wet silicon etchants including ordinary undoped tetramethyl ammonium hydroxide (TMAH)-water solution attack the overlaying aluminum metal interconnect during the anisotropic etching of (100) silicon. This paper presents a TMAH-water based etching recipe to achieve high silicon etch rate, a smooth etched surface and almost total protection of the exposed aluminum metallization. The etch rate measurements of (100) silicon, silicon dioxide and aluminum along with the morphology studies of etched surfaces are performed on both n-type and p-type silicon wafers at different concentrations (2, 5, 10 and 15%) for undoped TMAH treated at various temperatures as well as for TMAH solution doped separately and simultaneously with silicic acid and ammonium peroxodisulphate (AP). It is established through a detailed study that 5% TMAH-water solution dual doped with 38 gm/l silicic acid and 7 gm/l AP yields a reasonably high (100) silicon etch rate of 70 μm/h at 80 °C, very small etch rates of SiO₂ and pure aluminum (around 80 Å/h and 50 Å/h, respectively), and a smooth surface (±7 nm) at a bath temperature of 80 °C. The etchant has been successfully used for fabricating several MEMS structures like piezoresistive accelerometer, vaporizing liquid micro-thruster and flow sensor. In all cases, the bulk micromachining is carried out after the formation of aluminum interconnects which is found to remain unaffected during the prolonged etching process at 80 °C. The TMAH based etchant may be attractive in industry due to its compatibility with standard CMOS process.     

Multiuser Detection in SDMA–OFDM Wireless Communication System Using Complex Multilayer Perceptron Neural Network

The space division multiple access–orthogonal frequency division multiplexing (SDMA–OFDM) wireless system has become very popular owing high spectral efficiency and high load capability. The optimal maximum likelihood multiuser detection (MUD) technique suffers from high computational complexity. On the other hand the linear minimum mean square error (MMSE) MUD techniques yields poor performance and also fails to detect users in overload scenario, where the number of users are more than that of number of receiving antennas. By contrast, the differential evolution algorithm (DEA) aided minimum symbol error rate (MSER) MUD can sustain in overload scenario as it can directly minimizes probability of error rather than mean square error. However, all these classical techniques are still complex as these do channel estimation and multiuser detection sequentially. In this paper, complex multi layer perceptron (CMLP) neural network model is suggested for MUD in SDMA–OFDM system as it do both channel approximation and MUD simultaneously. Simulation results prove that the CMLP aided MUD performs better than the MMSE and MSER techniques in terms of enhanced bit error rate performance with low computational complexity.     

Scanning of sector and cosecant beams generated by a circular aperture

A method of scanning a one-dimensional shaped pattern generated by a circular aperture is presented. It is shown that the desired beam shape can be retained in the desired scan plane by superposing on the nonlinear phase distribution applied along and parallel to the meridian plane, a linear phase progression along the perpendicular direction. Analysis carried out using the stationary phase method of evaluating the integral reveals that the gradient of the linear phase progression is a function of position along the meridian plane of the aperture. Expressions for the phase functions are derived. Computed results on the phase distribution and the radiation pattern are presented.     

Routing Correlated Data in Wireless Sensor Networks: A Survey

Sensory data gathered from sensor nodes in physical proximity tend to exhibit strong correlation. To minimize such redundancy and hence curtail the load in wireless sensor networks with a goal to conserve energy, effective in-network fusion schemes have been extensively proposed in the literature. To this end, routing schemes supporting data fusion are extremely important as they dictate where and when sensory data streams shall intersect with each other and thus fusion will be performed. In this article we briefly articulate this problem and classify recently proposed routing schemes supporting data fusion in wireless sensor networks into three categories: routing-driven, coding-driven, and fusion-driven. We also give an overview of various algorithms in each category by summarizing their design approaches, benefits, and drawbacks.     

A model of front-illuminated n+-p-p+high-efficiency silicon solar cell

A realistic model of a front-illuminated n⁺-p-p⁺ silicon solar cell is developed by solving the current continuity equations for minority carriers in the quasi-neutral regions in steady state, assuming the light in the cell is trapped as a result of multiple reflections at the front and the back of the cell. This model is used to study the effects of the front emitter thickness and doping level and the light trapping on the J-V characteristic and thereby on the open-circuit voltage, short-circuit current density, curve factor, and the efficiency of the cell. A textured cell with an emitter thickness in the range of 0.3-1.0 μm with its doping ≈5×10¹⁸ cm^-3 and the recombination velocities of minority carriers as large as 200 cm/s at the n⁺ front surface and 10 cm/s at the back of the p base can exhibit an efficiency in excess of 26% (under AM 1.5 sunlight of 100 mW/cm² intensity) at 25°C if the light reflection losses at the front surface can be made small     

BIST/Digital-Compatible Testing of RF Devices Using Distortion Model Fitting

Testing of Radio Frequency (RF) circuits for nonlinearity specifications generally requires the use of multiple test measurements thereby contributing to increased test cost. Prior RF test methods have suffered from significant test calibration effort (training for supervised learners) when using compact tests or from increased test time due to direct specification measurement. On the other hand, due to aggressive technology scaling, there are plenty of digital transistors available that can be used to simplify testing of Analog/Mixed-Signal (AMS) and RF devices. In this paper, an RF test methodology is developed that: (a) allows RF devices to be tested for several distortion specifications using distortion model fitting algorithms in test time comparable to what can be achieved using supervised learning techniques while retaining the accuracy of direct specification measurement, (b) allows multiple RF specifications to be determined concurrently from a single data acquisition and (c) allows digital-compatible testing/BIST to be performed using digital testers or on-chip built in self-test (BIST) circuitry. With regard to (a), a key benefit is that no training of supervised learning algorithm is necessary. The proposed method based on distortion model fitting is shown to give excellent results across common RF performance metrics while providing ~10× improvements in test time compared to previous methods.     

Evaluation of post-fault restoration strategies in multi-domain networks

Although multi-domain survivability is a major concern for operators, few studies have considered the design of post-fault restoration schemes. This paper proposes two such strategies, based upon hierarchical routing and signaling crankback, to handle single and multi-link failure events in multi-domain IP/MPLS networks (also extendible to optical DWDM networks). Specifically, the hierarchical routing strategy relies upon abstracted domain information to compute inter-domain loose routes, whereas the crankback scheme applies signaling re-tries to restore paths in a domain-by-domain manner. The performance of these proposed solutions is then analyzed and compared via simulation.     

Metal Organic Framework Crystals in Mixed‐Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance

Mixed‐matrix membranes comprising NH₂‐MIL‐53(Al) and Matrimid or 6FDA‐DAM have been investigated. The metal organic framework (MOF) loading has been varied between 5 and 20 wt%, while NH₂‐MIL‐53(Al) with three different morphologies, nanoparticles, nanorods, and microneedles has been dispersed in Matrimid. The synthesized membranes have been tested in the separation of CO₂ from CH₄ in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH₂‐MIL‐53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, i.e., NH₂‐MIL‐53(Al) nanoparticles, into the highly permeable 6FDA‐DAM has a larger effect, and the CO₂ permeability increases up to 85% with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with a CO₂/CH₄ separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non‐destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modeling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by focused ion beam scanning electron microscopy analysis.     

Priority-based content processing with Q-routing in information-centric networking (ICN)

With exponential increase in the number of users and available data, service providers are facing hard times to satisfy and improve end user experience. Researchers have come up with the idea of exploiting increasing number of routers in a network, and it leads to the development of information-centric networking (ICN). Efficient usage of the in-network caches and content forwarding methodology are the key issues in an ICN architecture. ICN reduces average hop count and correspondingly average content download delay because the intra-domain routers in ICN have storage capacity and they can act as temporary content provider. In this paper, we address the content management issue in a cache with finite storage capability and propose an efficient content management policy that changes a router to a self-sustained cache. We propose a novel methodology to process content packets in the buffer of a cache and correspondingly reduce the propagation delay through a cache. We simulate our proposed algorithm over real-life network environment and evaluate the performance of different user experience metrics, e.g. average latency, throughput, goodput, and link load. Simulation results suggest that our proposed model outperforms the existing state-of-the-art on-path caching strategies.