Back Substrate Research Articles

Comparison of Single and Two-Photon Absorption for Laser Characterization of Single-Event Upsets in SOI SRAMs

The laser pulse energy thresholds for single-event upset measured by single photon and two photon absorption are measured and compared for Sandia SRAMs and DPSRAMs, and IBM 45-nm SRAMs for devices with and without the back substrate removed. These results are also compared to heavy-ion results taken on the same devices. Sandia SRAM data taken on different test dates resulted in considerably different TPA laser pulse energy thresholds even though the TPA system was calibrated using standard techniques each test date. These differences are believed to be due to changes in laser spot size. This shows that it is imperative to develop a calibration procedure that monitors all relevant laser parameters if TPA is to be used as a routine quantitative tool. Removing the back substrate makes a very large difference in TPA laser pulse energy threshold. This large difference is likely due to either displacement currents generated in the back substrate by TPA and/or nonlinear optical effects which can reduce the laser pulse irradiance in the active region. Nevertheless, the mechanism does not appear to affect the qualitative nature of TPA measurements. Both SPA and TPA laser measurements were used to estimate the heavy-ion threshold LETs of the Sandia DPSRAMs and 45-nm IBM SRAMs. Both SPA and TPA overestimated the heavy-ion threshold LET of the IBM 45-nm SRAMs (likely due to the large laser spot size compared to the size of the SRAM cell), but reasonably estimated the threshold LETs of the Sandia DPSRAMs. For the first time, TPA laser pulse energy (squared) is directly compared to SPA laser pulse energy at threshold. There is reasonable quantitative agreement between the charge required to induce upsets by TPA and SPA with the back substrate removed.

Electro-optical response of the combination of two twisted nematic liquid crystal cells in series and the applicability of the extended Jones matrix

A typical electro-optical response is observed by connecting two twisted nematic liquid crystal cells in series and placed back to back such that the director orientation on the back glass substrate of the first cell coincides with the director orientation of the front glass substrate of the second cell and vice versa. The two cells connected in series show cholesteric rotation. It is observed that for a given frequency the output transmittance oscillates having distinct maxima and minima with varying voltage and no flickering of transmittance have been observed at low frequencies. Variation of transmittance with frequency for given voltages is also reported and it has been found that increase of voltage at high frequency does not alter the transmittance appreciably. A discussion on the extended Jones matrix formulation and the scope of its applicability for this case is also given.

Analysis of the Metabolic Utilization of Carbon Sources and Potential Functional Diversity of the Bacterial Community in Lab‐Scale Horizontal Subsurface‐Flow Constructed Wetlands

Microorganisms are an integral part of the biogeochemical processes in wetlands. To improve the performance of constructed wetlands, it is very important to know the metabolic properties and functional diversity of the microbial communities. The purpose of this study is to analyze the metabolic properties and functional diversity of the microbial community in a horizontal subsurface-flow constructed wetland (CW) in a laboratory study through the sole-carbon-source utilization profiles using Biolog-ECO microplates. The technique has advantages over traditional cell culture techniques, such as molecular-level techniques-RNA amplification, which are time-consuming, expensive, and only applicable to the small number of species that may be cultured. This CW was designed to treat rural eutrophic water in China, using the plant L. This study showed that the metabolic activities of upper front substrate microorganisms (UF) were greater than those of the lower back substrate microorganisms (LB) in the CW. Integrated areas under average well color development (AWCD) curves of substrate microorganisms in the UF were 131.9, 4.8, and 99.3% higher than in the lower front part (LF), the upper back part (UB), and the LB part of the CW, respectively. Principal components analysis showed significant differences in both community structure and metabolic utilization of carbon sources between substrate microorganisms from different sampling sites. Carbon source utilization of polymers, carbohydrates, carboxylic acids, and amino acids was higher in UF than in LF, but that of amines and phenolic compounds was very similar in UF and LF. The richness, evenness, and diversity of upper substrate microbial communities were significantly higher than those of lower substrate. The LF substrate microbial communities had lower evenness than the other sampling plots, and the lowest richness of substrate microbial community was found in the LB part of the CW.

Novel Sensors Based on the Symmetry Properties of Split Ring Resonators (SRRs)

The symmetry properties of split ring resonators (SRRs) are exploited for the implementation of novel sensing devices. The proposed structure consists of a coplanar waveguide (CPW) loaded with movable SRRs on the back substrate side. It is shown that if the SRRs are placed with the slits aligned with the symmetry plane of the CPW, the structure is transparent to signal propagation. However, if the symmetry is broken, a net axial magnetic field can be induced in the inner region of the SRRs, and signal propagation is inhibited at resonance. The proposed structures can be useful as alignment sensors, position sensors and angle sensors. This novel sensing principle is validated through experiment.

Tilted Wave Lasers: A Way to High Brightness Sources of Light

Semiconductor laser diodes are conventionally based on a relatively thin waveguide structure grown epitaxially on a thick single crystalline substrate, wherein the latter serves as a medium for carrier flow and as mechanical support and plays no role in optics. Although earlier attempts to provide the outcoupling of light through a transparent substrate in leaky lasers realized a narrow leaky emission beam, either significant leakage losses led to the deterioration of the laser performance or/and a large fraction of the output optical power was concentrated in a co-existing angularly broad emission peak originating from the narrow active waveguide. Our solution, a tilted wave laser (TWL), includes polishing the back side of the substrate under the stripe providing mirror-like reflection for the leaky mode which can thus exhibit multiple reflection and amplification cycles before exiting the device from the substrate facet. Fulfillment of phase matching conditions allows wavelength-stabilized operation. At a wavelength of 1060 nm TWLs are shown to exhibit a very small thermal shift of the emission wavelength of 0.03 nm/K. A cw output power of 3.3 W for 2 mm long cavities with uncoated facets is obtained, wherein the entire power is concentrated in a single vertical lobe having a full width at half maximum of 0.8°. The scattering of the tilted optical wave by the back substrate surface roughness is modeled and found to be the main mechanism limiting the differential efficiency, wherein the scattering contributes up to 10 cm-1 to the losses for a present roughness of ~30 nm. The free carrier absorption in the n-doped substrate ( ~3 cm-1 for n ~1018 cm-3) dominates for a roughness <; 10 nm.

Direct Comparison of Charge Collection in SOI Devices From Single-Photon and Two-Photon Laser Testing Techniques

The amounts of charge collection by single-photon absorption (SPA) and by two-photon absorption (TPA) laser testing techniques have been directly compared using specially made SOI diodes. For SPA measurements and some TPA measurements, the back substrates of the diodes were removed by etching with XeF2. With the back substrates removed, the amount of TPA induced charge collection can be correlated to the amount of SPA induced charge collection. There are significant differences, however, in the amount of TPA induced charge collection for diodes with and without substrates. For the SOI diodes of this study, this difference appears to arise from several contributions, including nonlinear-optical losses and distortions that occur as the pulse propagates through the substrate, as well as displacement currents that occur only when the back substrate is present. These results illustrate the complexity of interpreting TPA and SPA single-event upset measurements.

Compact Elliptic-Function Coplanar Waveguide Low-Pass Filters Using Backside Metallic Patterns

In this letter, compact elliptic-function low-pass filters (LPF) implemented in coplanar waveguide technology by etching stepped impedance resonators (SIR) in the back substrate side, are presented. The required transmission zeros of the elliptic-function response are provided by the shunt connected SIRs. As an illustrative example, an order-3 prototype LPF with 1 GHz cutoff frequency is designed and fabricated. The measured stop-band rejection is better than 30 dB up to 6.4 GHz, and a narrow transition band is obtained. To demonstrate the possibilities of the approach to synthesize arbitrary elliptic-function responses and order, a fifth-order elliptic LPF with 1 GHz cut-off frequency is also designed and fabricated. Filter dimensions are as small as 6.6 mm × 9.2 mm, i.e, 0.034λ × 0.047A, for the third-order filter, and 12.1 mm × 13 mm (0.062λ × 0.067λ) for the fifth-order filter, λ being the guided wavelength at cutoff.

Controllable growth of (001) surface-oriented colloidal crystals by edge meniscus effect

Colloidal crystal films have been fabricated on silicon substrates using a flow-controlled vertical deposition (FCVD) method. Scanning electron microscopy shows that large areas of the colloidal crystal films can exhibit regular square arrangement or related 1×n superstructure induced by the surface relaxation of colloidal spheres. They are shown to be the (100) facing crystals of face centred cubic (FCC) structure. Their formation is related to meniscus bending at the edge of the wafer, which can be controlled by varying the width of the substrate or the wetting properties of the backing substrate. This (100) surface-oriented colloidal crystal could be used as a template to fabricate square arrangements of nanopore and nanodot arrays.

Solid-state compound phase formation of TiSi&lt;sub&gt;2&lt;/sub&gt; thin films under stress

In some investigations, TiSi grew simultaneously with TiSi2, Ti5Si4 and Ti5Si3, at temperatures between 400°C and 600°C. 11 Methods Samples with the structures SiO2/Si or Si3N4/Si , were chemically cleaned following a simple sequence. The following procedure was used: Samples were dipped, in sequence, in methanol, acetone, trichloroethylene, acetone and methanol, and then rinsed in ionised water. Finally, the samples were etched in a 20% solution of hydrofluoric acid to remove any native oxide layer that may be present. The role of the back side substrates, SiO2 and Si3N4, was to induce stress of different types during annealing. The samples were loaded in an ultra-high vacuum system where Ti of various thicknesses was deposited on the front side of the substrates. The vacuum during deposition was better than 6 × 10 –7

65nm Low Power (LP) SOI Technology on High Resistivity (HR) Substrate for WLAN and Mmwave SOCs

We present a 65nm RF SOI CMOS technology, targeted as Low Power (LP) to serve mobile applications. The integration has been made on High Resistive (HR) back substrate 300mm SOI wafers from SOITEC to improve performances in high frequency range, compared to bulk [1, 2]. For the first time, low leakage SRAM (Isb< 10pA at 0.9V, 25{degree sign}C, for 0.62µm2 and 0.52µm2 cells) are integrated on these HR wafers, and the paper reports a 30% power reduction in operation for a given maximum speed, compared to similar SRAM design on bulk. Furthermore, we have demonstrated a 21% measured power-delay product reduction compared to bulk, at 125{degree sign}C, on loaded ring oscillators.

A capacitive vibration-to-electricity energy converter with integrated mechanical switches

Due to recent advances in low-power VLSI design technology, it has become feasible to power portable or remote electronic devices by scavenging the ambient energy. The design, fabrication and measurement of a capacitive vibration-to-electricity energy converter are presented in this paper. With a device area constraint of 1 cm2 and an auxiliary battery supply of 3.6 V, the device was designed to generate an output power of 31 µW with an output saturation voltage of 40 V. An external mass of 4 g was needed to adjust the device resonance to match the input vibration of 2.25 m s−2 at 120 Hz. Mechanical contact switches were integrated onto the device to provide accurate charge–discharge energy conversion timing. The device was fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. Parasitic capacitance was minimized by partial back side substrate removal. Resonant frequencies of the fabricated device with and without the external mass agreed with the expected values. Without the external mass, the measured ac output power was 1.2 µW with a load of 5 MΩ at 1870 Hz. Detailed circuit modeling and ac output power measurement of the devices with the external mass attached are in progress.

Self-focused ZnO transducers for ultrasonic biomicroscopy

A simple fabrication technique was developed to produce high frequency (100 MHz) self-focused single element transducers with sputtered zinc oxide (ZnO) crystal films. This technique requires the sputtering of a ZnO film directly onto a curved backing substrate. Transducers were fabricated by sputtering an 18 mum thick ZnO layer on 2 mm diameter aluminum rods with ends shaped and polished to produce a 2 mm focus or f-number equal to one. The aluminum rod served a dual purpose as the backing layer and positive electrode for the resultant transducers. A 4 mum Parylene matching layer was deposited on the transducers after housing and interconnect. This matching layer was used to protect the substrate and condition the transfer of acoustic energy between the ZnO film and the load medium. The pulse-echo response for a representative transducer was centered at 101 MHz with a -6 dB bandwidth of 49%. The measured two way insertion loss was 44 dB. A tungsten wire phantom and an adult zebrafish eye were imaged to show the capability of these transducers.

A Flexible electronic‐paper display with an ultra‐thin and flexible LSI driver using quick‐response liquid‐powder technology

Abstract— A thin and flexible LSI driver with a thickness of less than 35 μm for a passive‐matrix‐driven Quick‐Response Liquid‐Powder Display (QR‐LPD™) was successfully mounted onto the flexible printed circuit (FPC) and the back substrates of a flexible QR‐LPD™. Amounted LSI driver on a plastic substrate shows no significant degradation in the driving performances and maintains physical flexibility without any connection failures. This technology can realize a fully flexible electronic paper in combination with a plastic‐substrate QR‐LPD™ fabricated by a roll‐to‐roll process.

An Indentation Technique to Characterize the Mechanical and Viscoelastic Properties of Human and Porcine Corneas

Cornea is a load-bearing tissue whose mechanical and viscoelastic characteristics are not well understood, due to the challenge associated with most of the measurements. A novel indentation technique has been developed for mechanical characterization of human and porcine corneal tissue, using a tailored depth-sensing microindentation instrument. During indentation, the corneas were suspended by clamping the edges of the cornea, thus allowing depth-sensing measurement free from the complication of the backing substrate. The deformation displacement and the amount of force applied by the indenter were used to obtain hysteresis and stress relaxation data for both human and porcine corneas. Optical coherence tomography was used to measure the thickness of the cornea. Simple theoretical analyses have been undertaken to explain the loading-unloading and the stress relaxation data. The effect of swelling on the mechanical properties of the cornea was also examined. Porcine corneas appeared to be less stiff and to demonstrate more linear response than human corneas under loading. More importantly, it is shown that swelling reduced the strength of the corneas. Our results demonstrate that this new indentation system can be used to characterize the mechanical and viscoelastic properties of corneas.

Self-Aligned Fabrication Process of Electrode for Organic Thin-Film Transistors on Flexible Substrate Using Photosensitive Self-Assembled Monolayers

A new long-wavelength-photosensitive self-assembled-monolayer (SAM) was developed, and a process fabricating alignment-free printable electrodes for flexible organic thin-film transistors (OTFTs) with the SAM was proposed. The SAM was degraded and its wetability was changed from hydrophobic to hydrophilic by irradiating it with UV light (>350 nm). The irradiated areas of SAM became more hydrophilic with tetramethylammonium hydroxide (TMAH) solution, which is a commercially available photoresist developer. Using the SAM and a back substrate exposure technique with TMAH rinsing, we can induce the self-alignment of solution-processed source/drain electrodes with respect to a gate electrode. A 20-µm-gap pattern of PEDOT was successfully formed by spin-coating on a plastic substrate.

MEMS design and fabrication of an electrostatic vibration-to-electricity energy converter

This paper presents a micro electrostatic vibration-to-electricity energy converter based on the micro-electromechanical system. For the 3.3 V supply voltage and 1 cm2 chip area constraints, optimal design parameters were found from theoretical calculation and Simulink simulation. In the current design, the output power is 200 μW/cm2 for the optimal load of 8 MΩ. The device was fabricated in a silicon-on-insulator wafer. Mechanical and electrical measurements were conducted. Residual particles caused shortage of the variable capacitor and the output power could not be measured. Fabrication processes are being refined to remove the back silicon substrate to eliminate residual particles and parasitic capacitance.

Fabrication and characterization of silicon nanowires with triangular cross section

Fabrication processes for silicon nanowires with triangular cross section are presented. Processes based on high resolution electron beam lithography and anisotropic etching have been developed on silicon on insulator substrates. As shown by numerical simulations, the triangular shape of the wire allows strong reduction of the dimensions by successive oxidation steps. Moreover, it is easy to define a gate on top of the wire that wraps the device and, with the back gate silicon substrate, allows the biasing of the structure on all sides. The conduction through the wire, as a function of the gate bias and for different temperatures, is reported and discussed.

Single-event upset in flip-chip SRAM induced by through-wafer, two-photon absorption

The single-event upset response of a single-event hardened SRAM 10-transistor cell is mapped in two dimensions via carrier injection by two-photon absorption through the back (substrate) surface in a flip-chip mounted 4 Mb SRAM. Using through-wafer carrier injection, charge is deposited into the active regions of the device at well-defined locations in a reproducible manner, and the single-event upset sensitive region of the device is localized to within /spl plusmn/0.3 micrometers.

Detecting art forgeries using LA-ICP-MS incorporating the in situ application of laser-based collection technology

The nature of art lends itself to forgery as a skilled and determined forger can mimic the techniques and styles of an artist to a level where even an expert can be duped. The authentication of paintings is a subjective process, but modern techniques may provide the means to provenance artist pigments based on elemental composition. This study applies laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to the analysis of artist paints from different manufacturers to identify variation between the elemental association patterns of these materials. The technique facilitates comparison of the paints used by an artist with produced works of art to assist provenancing initiatives of questioned materials. The effects of the trace element profiles of the backing substrate and binder on analytical data were also identified. By applying the technique to paint scraped from real paintings, a limited database was created to allow comparison to be made with some of Australian artist, Kathleen O’Connor's artworks and assist in determining production chronology. Data from this study were able to facilitate comparison of blue paints from two different paintings and confirm their co-provenance consequently determining the relative production date of a separate painting of previously unknown age. Preliminary trials of a prototype collection device designed to reduce damage and allow for in situ sampling of artworks were also undertaken. The device, which allows direct laser-based sampling of a complete painting, was tested using a Francis Ryan painting. The prototype allows for the collection of debris directly generated by LA-ICP-MS of a predefined area of a painting prior to subsequent analysis using direct LA-ICP-MS. This collection method significantly minimizes the amount of damage produced by conventional sampling methods. Analyses of the debris collected, using the prototype, were found to be comparable to the scrapings of equivalent paint analysed using direct LA-ICP-MS analysis.

Demonstration of single-event effects induced by through-wafer two-photon absorption

The first demonstration of through-wafer two-photon absorption (TPA) single-event effects (SEEs) testing is presented. We interrogate the single-event transient (SET) response of several different nodes of the LM124 operational amplifier via TPA carrier injection through both the front and back (substrate) chip surfaces. The results reveal that the SETs and sensitivities produced in several different nodes by front-side and back-side irradiation are effectively identical, confirming the validity of this approach for SEE studies.