Simple Test Structures Research Articles

The Detection of Open and Leakage Faults for Prebond TSV Test Based on Weak Current Source

During the manufacturing process of three-dimensional integrated circuits (3-D ICs), many defects may occur in through-silicon vias (TSVs). These defects affect the integrity of the signal passing through TSVs, therefore detecting these defects in the early production stage is crucial. This article proposed a built-in-self-test (BIST) method with a simple test structure and easily implemented fault detection process. Due to the fact that the defects in TSVs influence the charge/discharge speed of TSVs’ equivalent capacitance, a weak current source is designed as the central part of the proposed test structure, which can measure the TSVs’ charge/discharge speed and quantify it using digital values. The effectiveness and robustness of the proposed method is validated by HSPICE simulation. The minimum measurable fault, test time, and test circuit area are also assessed in this article. The simulation results show that the method this article proposed can detect weaker faults, compared with the traditional test methods.

Fundamental Investigation of Wave Propagation inside IC-Striplines upon Excitation with Hertzian Dipole Moments

To characterize the electromagnetic compatibility (EMC) of integrated circuits (ICs), especially the radiated emissions in the near field, transversal electromagnetic cell (TEM cell) or IC-stripline measurements (IEC 61967) are utilized. Due to the ongoing miniaturization and the increasing operating frequencies, accurate EMC characterization of ICs is becoming more important to achieve first-time-right designs. In order to avoid expensive redesigns, the prediction of these measurements in terms of a simulation workflow would be of high interest. Because of the high computational burden needed to conduct 3D full-wave finite element (FEM) simulations of both the device under test (DUT) and the measurement system, an equivalent representation of the DUT by means of analytical incident fields, such as Hertzian dipole moments, can be considered. In order to develop an order-reduced model of this kind, it is essential to have a solid understanding of the coupling and wave propagation effects inside the measurement systems. In the present paper, a fundamental investigation of the coupling paths between an IC-stripline and electric or magnetic dipole moments is presented and the results are compared to the existing analytical models. The results show that these analytical models, originally developed for TEM cells, are only partially valid for IC-striplines. It has also been shown that even for simple test structures, such as loop and monopole antennas, the representation in terms of one single dipole moment is insufficient.

A new mechanism for friction-induced vibration and noise

For years, friction-induced vibration and noise (FIVN) has puzzled many researchers in academia and industry. Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies, notably for automotive brake squeal, clutch squeal, and even rail corrugation. However, due to the complex and complicated nature of FIVN, there is not yet one fundamental mechanism that can explain all phenomena of FIVN. Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis (CEA) and transient dynamic analysis (TDA), this study attempts to propose a new fundamental mechanism for FIVN, which is the repeated cycles of partial detachment and then reattachment of the contact surfaces. Since friction is ubiquitous and FIVN is very common, the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.

A simple test structure for the electrical characterization of front and back channels for advanced SOI technology development

Pseudo-MOSFET delivers a fast, simple and reliable way of characterizing electrically SOI substrates without the need of full CMOS fabrication. However, the information refers to the back interface. Here, to probe the front interface, we extend the concept to a double-gate pseudo-MOSFET. The structure provides a pertinent test vehicle for the characterization and development of transistors channel and gate stack materials in a configuration similar to fully fabricated transistors. We show that the devices with undoped terminals need specialized modeling development to describe the double gate effect. Devices with doped terminals are immediately exploitable for parameter extraction.

Microcrystalline Silicon Tunnel Junction for Monolithic Tandem Solar Cells Using Silicon Heterojunction Technology

In this article, we developed a microcrystalline silicon tunnel junction to be used as a tunnel recombination junction between a large-gap top cell and a silicon heterojunction bottom cell, in a monolithic tandem integration. This junction is composed of a p-type layer on the top of an n-type layer, deposited by plasma-enhanced chemical vapor deposition at low temperature (200 °C). Microcrystalline phase percentage was controlled with Raman spectroscopy and ellipsometry measurements. The total stack has a thickness of 40 nm and an average conductivity around 10 S/cm. Minority carrier lifetime measurements showed an improvement of the field effect and the passivation with the addition of this junction on top of silicon heterojunction solar cells. Moreover, implementation of microcrystalline layer on top of reference rear emitter silicon heterojunction solar cells improved the fill factor and did not induce parasitic absorption above 700 nm. Simple test structures were fabricated in order to characterize the tunnel junction and optimize it. Then, we carried out dark temperature-dependent I-V measurements on those test structures and observed peaks and valleys, characteristic of the junction tunnel behavior. The developed tunnel junction shows low contact resistivity and activation energies; these are promising results for the complete integration on the tandem device.

A Simple and Robust Fabrication Process for SU-8 In-Plane MEMS Structures.

In this paper, a simple fabrication process for SU-8 in-plane micro electro-mechanical systems (MEMS) structures, called “border-bulk micromachining”, is introduced. It aims to enhance the potential of SU-8 MEMS structures for applications such as low-cost/disposable microsystems and wearable MEMS. The fabrication process is robust and uses only four processing steps to fabricate SU-8 in-plane MEMS structures, simplifying the fabrication flow in comparison with other reported attempts. The whole fabrication process has been implemented on copper-polyimide composites. A new processing method enables the direct, laser-based micromachining of polyimide in a practical way, bringing in extra processing safety and simplicity. After forming the polymeric in-plane MEMS structures through SU-8 lithography, a copper wet etching masked by the SU-8 structure layers is carried out. After the wet etching, fabricated in-plane MEMS structures are suspended within an open window on the substrate, similar to the final status of in-plane MEMS devices made from industrial silicon micromachining methods (such as SOIMUMPS). The last step of the fabrication flow is a magnetron sputtering of aluminum. The border-bulk micromachining process has been experimentally evaluated through the fabrication and the characterization of simple in-plane electrically actuated MEMS test structures. The characterization results of these simple test structures have verified the following process qualities: controllability, reproducibility, predictability and general robustness.

Intermediate layer-based bonding techniques for polydimethylsiloxane/digital light processing 3D-printed microfluidic devices

There is profound potential in developing novel microfluidic devices by integrating 3D-printed structures with polydimethylsiloxane (PDMS) to reap the advantages. One important aspect of the successful development of such microfluidic devices is to achieve a uniform and strong bond between PDMS and the 3D-printed structure. In this paper, we present the measurement results of the bonding strength between PDMS and digital light processing 3D-printed structures using intermediate layer-based bonding techniques. Five different intermediate layers were investigated: double-sided tape, a PDMS/tape composite, UV glue, (3-Aminopropyl) triethoxysilane (APTES), and sputter-coated SiO2. A simple burst test structure was designed and fabricated. Out of five available resins from the manufacturer, we chose the yellow resin to compare the bonding strengths with those intermediate layers. The burst test system consisted of a computer-controlled solenoid valve, pressure regulators, and a microscope for inspection. The sputter-coated SiO2 intermediate layer with a thickness of 77 nm demonstrated the highest bonding strength compared to other intermediate layers. The burst pressure with this SiO2 intermediate layer was greater than 436.65 kPa. Furthermore, we measured the burst pressure using the same SiO2 intermediate layer process for two other resins (emerald and black). The burst pressures for these were less than that of the yellow resin. The results indicate that the intermediate layer thickness and oxygen treatment processes have to be optimized for each resin.

Direct-Ink-Writing of Degradable Carboxymethylcellulose

Additive manufacturing with degradable polymers have recently drawn significant attention due to its promising biomedical applications including artificial tissue engineering, surgical, and orthopedic devices etc. This paper experimentally investigates the direct-ink-writing of one of the widely used degradable polymers, carboxymethlycellulose. Through printing and geometric characterization of simple test structures, effect of ink concentration, substrate material and direct-ink-writing process parameters including printing pressure, printing speed and nozzle substrate distance on the process outcome is studied. Preliminary findings on printing of micro-scale structures using nozzles as small as 10 μm in diameter are also presented.

An Empirical Model for Predicting SE Cross Section for Combinational Logic Circuits in Advanced Technologies

At the gigahertz range of frequencies, contribution of combinational logic upsets has increased significantly to the overall single-event (SE) upset rate (SER) of sequential circuits. Most approaches for modeling and/or predicting logic SER are either pure simulation based or pure experiment based. Simulation-based approaches need a lot of computing power. Experiment-based approaches require fabrication of actual circuits. This paper presents an empirical method that uses experimental data from simple test structures for estimating SE vulnerability of any combinational logic circuit. Estimated logic SEU cross section matches well with the measured logic SEU cross section. Estimated logic SEU cross section results obtained with the proposed method are within $2\times $ average error when compared to the experimentally measured logic SEU cross section. This method only needs to be calibrated once for use at a given technology node.

Probing Interface Defects in Top-Gated MoS2 Transistors with Impedance Spectroscopy.

The electronic properties of the HfO2/MoS2 interface were investigated using multifrequency capacitance-voltage (C-V) and current-voltage characterization of top-gated MoS2 metal-oxide-semiconductor field effect transistors (MOSFETs). The analysis was performed on few layer (5-10) MoS2 MOSFETs fabricated using photolithographic patterning with 13 and 8 nm HfO2 gate oxide layers formed by atomic layer deposition after in-situ UV-O3 surface functionalization. The impedance response of the HfO2/MoS2 gate stack indicates the existence of specific defects at the interface, which exhibited either a frequency-dependent distortion similar to conventional Si MOSFETs with unpassivated silicon dangling bonds or a frequency dispersion over the entire voltage range corresponding to depletion of the HfO2/MoS2 surface, consistent with interface traps distributed over a range of energy levels. The interface defects density (Dit) was extracted from the C-V responses by the high-low frequency and the multiple-frequency extraction methods, where a Dit peak value of 1.2 × 1013 cm-2 eV-1 was extracted for a device (7-layer MoS2 and 13 nm HfO2) exhibiting a behavior approximating to a single trap response. The MoS2 MOSFET with 4-layer MoS2 and 8 nm HfO2 gave Dit values ranging from 2 × 1011 to 2 × 1013 cm-2 eV-1 across the energy range corresponding to depletion near the HfO2/MoS2 interface. The gate current was below 10-7 A/cm2 across the full bias sweep for both samples indicating continuous HfO2 films resulting from the combined UV ozone and HfO2 deposition process. The results demonstrated that impedance spectroscopy applied to relatively simple top-gated transistor test structures provides an approach to investigate electrically active defects at the HfO2/MoS2 interface and should be applicable to alternative TMD materials, surface treatments, and gate oxides as an interface defect metrology tool in the development of TMD-based MOSFETs.

A combined surface and bulk TCAD damage model for the analysis of radiation detectors operating at HL-LHC fluences

In this work we present the development and the application of a new TCAD modelling scheme to simulate the effects of radiation damage on silicon radiation detectors at the very high fluence levels expected at High Luminosity LHC (up to 2 × 1016 1MeV n/cm2). In particular, we propose a combined approach for the analysis of the surface effects (oxide charge build-up and interface trap states introduction) as well as bulk effects (deep level traps and/or recombination centers introduction). Experimental measurements have been carried out aiming at: i) extraction from simple test structures of relevant parameters to be included within the TCAD model and ii) validation of the new modelling scheme through comparison with measurements of different test structures (e.g. different technologies) before and after irradiation. The good agreements between experimental measurements and simulation findings foster the suitability of the TCAD modelling approach as a predictive tool for investigating the radiation detector behavior at different fluences and operating conditions. This would allow the design and optimization of innovative 3D and planar silicon detectors for future HL-LHC High Energy Physics experiments.

Field-Testing of Structure on Shallow Foundation to Evaluate Soil-Structure Interaction Effects

A simple test structure was designed and constructed to facilitate forced-vibration testing of a shallow foundation experiencing combined base shear and moment demands. The structure consists of a reinforced concrete foundation and top slab separated by steel columns that can be configured with braces. The slabs have a 2:1 aspect ratio in plan view to facilitate variable amount of overturning for shaking in orthogonal directions. The structure was transported to two field sites with representative shear-wave velocities of approximately V S = 95 m/s and 190 m/s. At each site, the foundation slab was cast-in-place. Forced vibration testing was conducted over a wide range of frequencies and load levels to enable the evaluation of foundation-soil stiffness and damping behavior for linear and nonlinear conditions. The data collected to facilitate such analyses include acceleration, displacement, and foundation pressure records (data can be accessed at DOI: 10.4231/D3NK3658M, DOI: 10.4231/D3HT2GC4G, DOI: 10.4231/D3D21RK0N).

Setup for laboratory studies of the environmental conditions influence on the fixed charge state in silicon dioxide

The position sensitive detectors operate in high intensity radiation field of the collider experiment [1]. Important task is to estimate the influence of different radiation effects on properties of the detector. We focus on the laboratory studies to estimate the reliability of different types of silicon detectors. We use the simple test structures produced by standard technology for the silicon detectors. We give the primary attention to the case when the depth of active detector region varies from 10 to 20 μ m because it leads to the most significant influence of SiO2-Si interface on processes in silicon bulk. We present the experimental results of long term irradiation test with Am241 (one year). Influence of the environmental conditions on the fixed charge states in silicon dioxide was investigated using developed simple model.

Investigation of Buffer Traps in AlGaN/GaN Heterostructure Field-Effect Transistors Using a Simple Test Structure

We propose a new method which can extract the information about the electronic traps in the semi-insulating GaN buffer of AlGaN/GaN heterostructure field-effect transistors (HFETs) using a simple test structure. The proposed method has a merit in the easiness of fabricating the test structure. Moreover, the electric fields inside the test structure are very similar to those inside the actual transistor, so that we can extract the information of bulk traps which directly affect the current collapse behaviors of AlGaN/GaN HEFTs. By applying the proposed method to the GaN buffer structures with various unintentionally doped GaN channel thicknesses, we conclude that the incorporated carbon into the GaN back barrier layer is the dominant origin of the bulk trap which affects the current collapse behaviors of

Doped Layer Optimization for Silicon Heterojunctions by Injection-Level-Dependent Open-Circuit Voltage Measurements

Besides passivation of the c-Si absorber, provided mainly by the undoped buffer layer, the net doping of the silicon thin films plays a major role in the performance of silicon-based heterojunction (SHJ) solar cells. However, junction engineering is complex as high net doping often interferes with the interface passivation and the optical properties of the silicon thin films. We show that injection-level-dependent open-circuit voltage (Suns- Voc) measurements are a simple and valuable method for the characterization and optimization of the doped amorphous silicon (a-Si:H) layers. It is shown by experiment and device simulations that at high illumination intensities the Suns- Voc characteristic exhibits a strong signature of defect recombination within the a-Si:H, which is determined by the a-Si:H doping and the interfacial transparent conducting oxide (TCO) properties. This fact is exploited for a qualitative interpretation of the interplay between a-Si:H and the interfacial TCO properties. As a clear correlation between the Suns- Voc characteristic and the maximum power point conditions of the devices exists, fill factor (FF) losses attributed to the doped a-Si:H and the interfacial TCO properties can 1) be easily predicted in the early stage of device optimization on simple test structures, or 2) these FF losses can be identified and distinguished from other FF losses in the final device.

Improved Frequency Response in a SiGe npn Device through Improved Dopant Activation

We study the impact of improved dopant activation in a BiCMOS SiGe technology, using laser annealing to improve activation, and a low temperature contact module to avoid de-activation. We present the results of simple DC test structure measurements and high frequency bipolar transistor measurements. Improved activation significantly reduces sheet resistance, particularly for polysilicon layers. Likewise, reductions in the bipolar device resistance parasitics cause an improvement in maximum power gain frequency (fMAX).

Accurate Method of Measuring Specific Contact Resistivity of Interface between Silicide and Silicon and Its Application

Reduction of specific contact resistivity is one of the key items for downscaling of device feature size. This paper discusses an accurate method of measuring specific contact resistivity by using our simple four-point probe test structure having a small area, the interface resistance of which is to be measured, fabricated on a substrate that has low sheet resistance. We also show its application for direct specific contact resistivity measurements of several systems that have dopant dependence, i.e., the NiPtSi/Si, NiPtSi/SiGe, and Pt silicide systems, as well as the metal-metal system between silicide and contact plug metal.

A Simple Test Structure for Evaluating the Variability in Key Characteristics of a Large Number of MOSFETs

The increase in the electrical characteristic variability of MOSFETs caused by the miniaturization of MOSFETs is one of the critical issues for realizing the low power consumption of large-scale-integrated circuits and the high accuracy of analog devices. It is necessary to easily evaluate the variability of a very large number of MOSFETs in a very short time for short-period-developing fabrication processes and device structures. We have proposed and developed a simple test structure for evaluating the electrical characteristics of over 1.2 million MOSFETs such as threshold voltage (Vth), subthreshold swing (S-factor) in around 30 min. The accuracy of the test circuit developed is 1.9 mV, as 3σ. We have also evaluated the Vth distribution, the S-factor distribution, and the dependence of Vth variability on the gate size and antenna ratio of MOSFETs. The measurement results are very useful in developing fabrication processes, process equipment, and device structures, that suppress the variability.

Precision Jetting of Glob Top Materials – a methodology for process optimization

During the last years, jetting processes for higher viscosity materials have gained widespread interest in microelectronics manufacturing. Main reasons for this interest are high throughput/productivity of jetting, contactless material deposition, high volume precision and freely designable deposition patterns. In previous studies we have demonstrated the jetability of different resin-based materials, being exemplary for unfilled adhesive, for low viscous Underfill resin and for higher viscosity Glob Top materials. The focus of our previous work was on the dosing of Underfill material, where this study is dealing with more complex materials – Glob Top resins. These materials are non-Newtonian fluids - the flow curves of the filled materials can be described by models of Cross or Herschel/Bulkey. Furthermore, highly filled and paste-like mixtures show a significant time dependency of formation of structural equilibrium after deformation, so process development needs to take this into account, so detailed material analysis is described within this study. To illustrate the potential of jetting as a flexible and powerful tool for Chip on Board encapsulation, both, simple test-structures (dots, lines, dams) but also more complex demonstrators have been assembled using wire bonded ICs on ceramic substrates and encapsulants showing viscosities ranging from 10 Pas to > 100 Pas. Not only basic process data on droplet diameter, resulting material depot size and positioning accuracy have been evaluated, but also statistical means have been employed to determine process homogeneity and stability depending on the respective parameter set. Additionally, the whole process was followed by a high-speed camera system, providing detailed information on actual jetting behaviour during droplet release, flight and impact. Summarized this paper gives a detailed insight into jet process development for high viscosity Glob Top materials and describes process design rules and limitations and thus allows the optimized use of advanced jetting technology for Chip on Board assemblies.

Distributed Conversion of Common-Mode Into Differential-Mode Interference

In this paper, the mechanisms that lead to the conversion of common-mode (CM) RF interference (RFI) into differential-mode (DM) disturbances, which corrupt the information content of nominal signals and impair the operation of electronic systems, are investigated. To this purpose, distributed and lumped common-mode into differential-mode (CM-DM) conversion mechanisms are discussed with reference to a simple test structure that can be analytically described. On the basis of the proposed analysis, the origin and the relative impact of such mechanisms is highlighted and the detrimental effect of distributed CM-DM conversion on the effectiveness of differential RFI suppressing filters is discussed. Theoretical predictions are compared with experimental results.