Capacitor Test Structures Research Articles

Destructive dielectric breakdown of 2D muscovite mica

This study investigates the destructive breakdown (DBD) phenomenon in the van der Waals gate dielectric 2D muscovite mica (4–12 nm thick), focusing on its electrical reliability as a gate dielectric material. Capacitor test structures were electrically stressed, and the resulting impact on the physical structure was analyzed using atomic force microscopy. The volume of material removed in a DBD event is found, and the energy required (Ereq) to vaporize the volume was calculated. It is found that Ereq is proportional to the average electrical energy dissipated in the capacitor during breakdown (BD), indicating a direct correlation between damage caused during DBD and the current flow at BD location. In contrast to other thin film dielectrics, the 2D mica is highly susceptible to DBD even at very low current density (<1 A/cm2) and the abrupt, destructive BD more resembles that of thick film dielectric breakdown. An explanation for these finding is proposed in which intercalated K+ ions agglomerate around defects generated by the electrical stressing such that the defect density increases substantially in the local vicinity of BD locations, which leads to increased current and associated Joule heating after the BD event.

Toward Energy‐Efficient Ferroelectric Field‐Effect Transistors and Ferroelectric Random Access Memories: Tailoring the Coercive Field of Ferroelectric HfO2 Films

Many modern applications require fast and reliable nonvolatile memory. Ferroelectric (FE) memories, such as FE field‐effect transistors and FE random access memories, show great promise in meeting these requirements. Another key factor is power efficiency. In the case of FE memories, the coercive field is a critical parameter for improving power consumption. This article introduces and reviews four promising methods to tailor the of FE films based on Zr‐doped : 1) composites with various Hf contents, 2) hybrid stacks consisting of antiferroelectric sublayers with excess Zr (x 0.5) and FE sublayers, 3) superlattice structures (also known as nanolaminates) consisting of and sublayers stacked on top of each other, and 4) films doped with an aluminum impurities. Electrical characterization of metal–FE–metal capacitor test structures confirms the suitability of all approaches. Analysis of the strengths and weaknesses is conducted, considering the tuning range, shape stability of the polarization versus electric field hysteresis loop, and the impact of these approaches on the remanent polarization .

Channel characteristics of ferroelectric organic High-K dielectric asymmetric metal insulator semiconductor capacitor

In the present work, it is demonstrated that an asymmetric organic MIS (AMIS) capacitor utilizing sandwiched ferroelectric material between high k-dielectric as an insulator and pentacene as an active semiconductor can be used for a wide range of sensing applications. The capacitive test structure is simpler in fabrication and characterization and is less sensitive to defect states since it utilizes a strong accumulation region. The polarization behavior of the ferroelectric materials enables higher charge density in the channel thereby reducing channel resistance and thus increasing the channel capacitance. This property of the Ferro-based AMIS structure enables the extraction of OTFT parameters and also serves as a platform for sensing applications. The use of high-k dielectric material both as an insulator and buffer layer makes the technique more robust against lattice mismatch and high-power dissipation. The channel characteristics are free from the contact resistance effect due to the large characteristics channel length at a smaller frequency that makes the technique unique. 2-D numerical simulation with Pentacene/Ferro geometry and gold/ITO as top/bottom contact configuration has been simulated to demonstrate the concept and the model. (a) C-V without high k dielectric and without ferro, (b) C-V only with high k dielectric and (c) C-V with high k dielectric and with ferro material. • The channel capacitance of the conventional AMIS structure can be increased significantly by employing a ferroelectric material. • This property can be suitably used for extracting accurate TFT channel properties and also for sensing applications.

Characterization of Process-Induced Nonuniformity Using Asymmetric Metal–Insulator–Semiconductor Capacitive Test Structure

For most large-area applications, spatial nonuniformity of transistor characteristics makes it difficult if not impossible, to achieve adequate performance. Nonuniform parameters may lead to variations in color or gray level, which is commercially not viable. A variation in threshold voltage, mobility or I-V characteristics of an organic thin-film transistor (OTFT) in a pixel circuit can result in unacceptable variation in the current driving the organic light-emitting diode (OLED) which accounts for large nonuniformities in the pixel brightness. Given its importance, a fast and straightforward method for characterization of device variations would be of great help in the process development and optimization. In the present work, a simple, easy to fabricate two-terminal asymmetric metal- insulator-semiconductor (AMIS) capacitive test structure is proposed for quick and accurate characterization of the process-induced nonuniformities in mobility, threshold voltage, and drain current. The capacitance-voltage (C-V) characteristic of the proposed AMIS structure is derived mostly from the channel, and its contribution to the total capacitance at any given frequency depends on channel properties including mobility and threshold voltage. At low frequencies, the C-V characteristics become independent of the series resistances, and hence, complex techniques can be sidestepped for accurate estimation of channel properties. The simulation results are presented to demonstrate the concept using a single AMIS test structure. The experimental results obtained with top contact pentacene based on AMIS arrays are presented to show the concept and advantages of the proposed structure.

Characterization and Deembedding of Negative Series Inductance in On-Wafer Measurements of Thin-Film All-Oxide Varactors

A fast dielectric characterization method is on-wafer probing of circular, capacitive test structures. However, this was found to be accurate only for limited frequencies in the megahertz range. At higher frequencies, the measured impedance data deviate from the expected characteristic. The effective capacitance shows a negative slope, although it should increase up to infinity at electrical resonance. This prevents from extracting accurate material data at RF frequencies. The modeling of this phenomenon as an appealing negative series inductance is presented, as well as the robustness of its compensation. The resulting wide-frequency fitting additionally enables the characterization of the bottom electrode material. This compensation is applied to measurements of the recently presented all-oxide varactor based on the conducting oxide SrMoO3 (SMO). Previously, only independent conductivity measurements for nonintegrated SMO thin films were available. This compensation now allows for a valid confirmation of the low expected resistivity $45~\mu \Omega \text {cm}$ of integrated thin films.

Combined experimental and numerical approach to study electro-mechanical resonant phenomena in GaN-on-Si heterostructures

Due to the intrinsic piezoelectric nature of Gallium Nitride (GaN), devices manufactured with such technology are in principle prone to experience electro-mechanically induced resonance phenomena under operating conditions. In this paper, we present the thorough approach combining simulation and experiment to study the occurrence and implications of such electro-mechanical resonances. A simple GaN-on-Si capacitor test structure was fabricated and electrically excited in order to activate the mechanical eigenmodes of the assembly which are measured by a Laser-Doppler-Scanning-Vibrometer. A multiphysics Finite Element (FE) model of the tested structures was built in order to perform harmonic analysis and to quantitatively study the effects of damping on displacement, stress and strain. A mathematical comparison on different aspects between the model and measurements show good agreement. This successfully verifies the methodology to model the dynamic resonance behaviour of piezoelectric active chips.

Effect of crystallinity on microwave tunability of pulsed laser deposited Ba0.5Sr0.5TiO3 thin films

Barium Strontium Titanate (Ba0.5Sr0.5TiO3) thin films on (100) oriented MgO substrates were deposited by Pulsed Laser Deposition (PLD) technique. The deposition temperature of 750°C is kept constant and the oxygen working pressure is varied from ~1×10−1mbar to 1×10−4mbar. The X-ray diffraction pattern shows that higher oxygen working pressure deposited films are partially crystalline. The lower oxygen working pressure (1×10−4mbar) deposited films showed improved crystallinity. The crystallinity is further increased with a particular orientation as the laser fluence increased from 1.4J/cm2 to 2J/cm2.The microwave dielectric properties of these films were measured using Inter Digitated Capacitor (IDC) test structure. It is found that the maximum tunability (in IDC configuration) of 16.5% at 1GHz is obtained for oxygen working pressure and high fluence (1×10−4mbar and 2J/cm2) deposited films, whereas the other films tunabilities are in the range of 1–2% only. These studies also help us to explore the correlation between structure and microwave dielectric properties. Hence, in the present study the 1×10−4mbar and 2J/cm2 deposition conditions are found to be more helpful in unleashing conditions that lead to better tunability in Ba0.5Sr0.5TiO3 films.

Estimation of carrier mobility at organic semiconductor/insulator interface using an asymmetric capacitive test structure

Mobility of carriers at the organic/insulator interface is crucial to the performance of organic thin film transistors. The present work describes estimation of mobility using admittance measurements performed on an asymmetric capacitive test structure. Besides the advantage of simplicity, it is shown that at low frequencies, the measured capacitance comes from a large area of channel making the capacitance-voltage characteristics insensitive to contact resistances. 2-D numerical simulation and experimental results obtained with Pentacene/Poly(4-vinyphenol) system are presented to illustrate the operation and advantages of the proposed technique.

Direct Mismatch Characterization of Femtofarad Capacitors

Reducing the capacitance of programmable capacitor arrays (PCAs), commonly used in analog integrated circuits, is necessary for low-energy applications. However, limited mismatch data are available for small capacitors. We report mismatch measurement for a 2-fF poly–insulator–poly (PIP) capacitor, which is the smallest reported PIP capacitor to the best of the authors' knowledge. Instead of using complicated custom on-chip circuitry, direct mismatch measurement is demonstrated and verified using Monte Carlo simulations and experimental measurements. Capacitive test structures composed of 9-bit PCAs are implemented in a low-cost 0.35- $\mu\text{m}$ CMOS process. Measured data are compared to the mismatch of large PIP capacitors, theoretical models, and recently published data. Measurement results indicate an estimated average relative standard deviation of 0.43% for the 2-fF unit capacitor, which is better than the reported mismatch of metal–oxide–metal (MOM) fringing capacitors implemented in an advanced 32-nm CMOS process.

Dielectrics for Power Capacitors

High voltage capacitors are key components for transient storage and release of electrical energy in mobile electric devices, electric vehicles, stationary power systems and power transmission. Due to their high electric breakdown voltage, self-healing capability and affordability, polymer-based film capacitors are widely used, particularly those made from biaxially oriented polypropylene (BOPP). Their maximum operating temperature near 100°C, however, requires careful thermal management and oversize design. In high temperature applications well above 200°C, the preference shifts from organic to ceramic dielectric materials. Multilayer ceramic capacitors (MLCCs) are known for their excellent mechanical and thermal robustness, have a mature fabrication technology and have found a wide spectrum of applications in power electronic systems. Their higher cost level is frequently over-compensated by their robustness, a unique selling point particularly in high temperature applications. The present investigation deals with the suitability of various ceramic materials like mica, several high and low temperature sinterable tapes (HTCC, LTCC) as well as atmospheric plasma-sprayed (APS) alumina under such conditions. Aspects of manufacturability and component design are taken into account as well. Dielectric materials performance is particularly addressed by high temperature impedance spectroscopy up to several hundred °C to minimize further self heating of the components above the operating temperature. Although these materials, commercial as well as non-commercial ones, were originally developed for either electric or high temperature applications, the analysis suggests promising materials choices also in cases, when both requirements come together. Although dissipation factors obtained from capacitive test structures cover a wide range, capacitors made from pure alumina (HTCC) generally have lower dielectric loss at all temperatures than those made from glass-ceramic composites (LTCC). Quite diverse properties are obtained with APS alumina, which would represent a promising fabrication alternative due to the possible solid deposition on metal surfaces.

Biomolecule Detection Using a Resonant Capacitive Sensor

Biomarker detection is of paramount importance to the medical community for the assessment of health and human performance. Two biomarkers of interest are orexin A (a biomarker of cognitive function) and trimethylamine (a biomarker of the disease trimethylaminuria). For the purpose of orexin A and trimethylamine detection, resonant capacitive sensors with a peptide functionalized guanine dielectric layer are designed and fabricated, Figure 1. The molecular recognition peptides, Table 1, selectively capture the biomarkers. The binding of the biomarkers to the peptides changes the permittivity of the dielectric layer resulting in a significant shift in the resonant frequency, amplitude, and phase of the sensors thereby indicating the biomarkers’ presence. Due to the limited utilization of guanine in electronics, the first objective in designing these sensors has been guanine characterization. For characterization purposes, guanine was deposited as the dielectric layer in a capacitive test structure (CTS), and from these structures, the dielectric constant and loss tangent of guanine was determined by comparing the measured scattering-parameters (S-parameters) to an electrical model of the device. Subsequently, guanine was deposited as the dielectric for the resonant capacitive sensor to determine the resonance of the guanine-integrated structure and to serve as the sensor platform. After guanine characterization, the next objective is to investigate methods for peptide functionalization. The two methods of interest are spin-coating and chemical tethering (preferred). In order to be successful, the peptides must adhere to the guanine in a manner that does not interfere with the biomarker binding sites. The chemical tethering method offers a way to covalently cross-link the peptides to the guanine, but the spin-coating is less likely to interfere with the peptides’ binding sites. After determining a functionalization method, the guanine will be functionalized with peptides using this method. The final objective is to test the fabricated sensors. For testing, the S-parameters are measured to determine the resonance of the sensors pre-exposure (baseline) and following exposure to positive (orexin A in aqueous phase and trimethylamine in vapor phase) and negative controls. Acknowledgements: Support was provided through the Dayton Area Graduate Studies Institute Fellowship, and the Air Force Research Laboratory (Human Effectiveness and Materials and Manufacturing Directorates).

Electrical characterization of top-gated molybdenum disulfide metal–oxide–semiconductor capacitors with high-k dielectrics

Top-gated metal–oxide–semiconductor (MOS) capacitor test structures were fabricated with 30nm HfO2 and Al2O3 thin films by atomic layer deposition (ALD) on surface-functionalized, bulk molybdenum disulfide (MoS2), and characterized with C–V and I–V measurements. The C–V results showed significantly different behavior for MoS2 samples compared to conventional Si MOS capacitors, where the area dependence, frequency dependence, and hysteresis results demonstrate the possibility of different properties of high-k dielectrics on MoS2. The C–V frequency dispersion suggests the existence of defects in the interfacial region of the high-k/MoS2.

Ba(ZrxTi1−x)O3 thin films for tunable microwave applications

Ba(ZrxTi1−x)O3 (BZT) thin films were deposited on (100)MgO substrates by RF-magnetron reactive sputtering using metal targets. Coplanar capacitor test structure with Pt/Au electrode based on BZT/MgO layer was fabricated by sputtering, photolithography, and etching processes. 500-nm-thick BZT thin films for high frequency performance showed a single perovskite phase and a high crystallinity on the MgO substrate with only a (001)/(100) orientation at an optimum deposition conditions. The BZT films had a stoichiometric Ba/Ti ratio and epitaxially grew on the MgO substrate. They showed a dense microstructure without cracks or voids. Dielectric properties of BZT thin film (x=0.26) showed little dispersion at 1–18GHz. Moreover, low frequency dielectric properties have been characterized using coplanar capacitor structures in a temperature range of −180 to 120°C. This film showed the high temperature stability of capacitance and loss tangent. These results indicated that we succeeded in depositing high-quality and potentially tunable ferroelectric BZT films for high-frequency applications by RF-magnetron reactive sputtering using metal targets.

Reliability Performances of BST Capacitors for Impedance Tuning Applications

STMicroelectronics recently developed a solution of integrated tunable capacitor based on BST material, which offers excellent RF performances, low power consumption and high linearity required in adaptive radiofrequency tuning applications. This paper focuses more particularly on the development of a predictive reliability model established from highly accelerated tests performed directly at wafer level on dedicated capacitor test structures. The validity of such model, representative of Time-Dependent Dielectric Breakdown (TDDB) failure mechanism, was confirmed by additional package level reliability tests, carried out on final product samples. The lifetime predictions provided by the model turn out to be perfectly compliant with RF tunable applications, considering typical mission profiles for such products.

Capacitance and $S$-Parameter Techniques for Dielectric Characterization With Application to High-$k$ PMNT Thin-Film Layers

This paper presents a method for measuring the complex permittivity of a dielectric material on a dielectric/metal stack without etching the dielectric layer. A series of circular capacitor test structures were designed and fabricated. For the first time, the unwanted capacitance Cp, which is formed by the oxide layer between the bottom metal layer and the silicon substrate, was defined and systematically investigated. The technique is shown to be suitable for characterization of a lead magnesium niobate-lead titanate (PMNT) material on the complex cross sections involved in the development of a novel high-k material. An extremely high- k of 1115 (high capacitance density of 26 fF/μm2) for a PMNT metal-insulator-metal (MIM) capacitor was achieved. In addition, low leakage current density of 2 × 10-10 A/cm2 and low loss tangent were also obtained. These results clearly showed that the PMNT MIM capacitors are very promising for both decoupling and more general RF and mixed-signal applications until the year 2020, according to the International Technology Roadmap for Semiconductors (ITRS).

Glass polarization induced drift in microelectromechanical capacitor

We present a quantitative physical model for glass substrate polarization and study the glass polarization by measuring the capacitance drift from microelectromechanical capacitor test structure. The model consists of mobile and immobile charge species, which are related to alkali metals and non-bridging oxygen in glass. The model explains consistently our results and the previously observed non-homogeneous charging effect in a radio-frequency switch fabricated on a glass substrate. The results indicate that the bulk properties of the glass layer itself can be a significant source of drift. The modeling allows estimation of the drift behavior of the several kinds of device structures.

SiGe MEMS at processing temperatures below 250 °C

This work demonstrates, for the first time, the use of a post deposition laser annealing technique to realize operational SiGe MEMS devices at deposition temperatures as low as 210°C. The patterned amorphous SiGe layers are treated by an excimer laser to induce crystallization. After the laser treatment, SiGe devices with good electrical and mechanical properties, such as contact resistivity values to a TiN electrode as low as 4.9×10−7Ωcm2 and a strain gradient of −1.6×10−6μm−1, are obtained. Devices such as an array of functional capacitive test structures and capacitive switches are realized.

Evaluations of intrinsic time dependent dielectric breakdown of dielectric copper diffusion barriers

Study of the intrinsic time dependent dielectric breakdown (TDDB) of dielectric copper diffusion barriers was realized using a unique planar capacitor (Pcap) test structure. The test vehicle has several advantages over the metal dot method. The most important one is the elimination of field enhancement effect which could be more than 50% in the case of metal dots. In order to test the effectiveness of this test vehicle, two different dielectric barriers, one conventional SiCN film and the other a BN film still under development, were selected for TDDB evaluations. Significant differences were observed between the two films in TDDB lifetime, the shape parameter β of the Weibull failure time distributions, and the characteristics of the current versus time curves. The BN film had a degradation of more than four orders of magnitude in TDDB lifetime than SiCN. The Weibull shape parameter β of SiCN was 8.4, among the highest values that have been reported for any dielectric barrier films, versus 1.4 for the boron nitride film. Furthermore, the SiCN film showed a decrease in current versus time curves during the initial stage of the stressing, a trend which is typically related to charge trapping in defect-free films. This was not the case for the BN film where the leakage currents were much higher. The results demonstrate that the Pcap test structure is an effective vehicle to evaluate the intrinsic reliability of dielectric barrier films.

Aluminum Nitride piezo-MEMS on polyimide flexible substrates

In this work the micro-fabrication of flexible MicroElectroMechanical transducers based on the piezoelectric effect is reported. We developed the technological protocol to realize a piezoelectric transducer composed by a Molybdenum (Mo) top electrode, the Aluminum Nitride active layer and a Mo bottom electrode on a polymeric tape. The process starts from the DC sputtering deposition of the Molybdenum layer at room temperature on Kapton HN. The Molybdenum is chosen not only for its electrical properties but also because it enhances the crystal orientation of AlN. The next step is the deposition of AlN that occurs at high temperature, around 250°C. Temperature and physical sputtering enhanced by applying a DC bias on the substrates are two important parameters to improve the crystal orientation of the film. These extreme growth conditions guarantee a very good crystal structure without damaging the Kapton substrate. Then a final Mo layer is sputtered at room temperature. SU8-25 thick photo resist is used to define the top electrode and the AlN layer, and in a second mask step the Mo bottom electrode. The developer, the PG remover and SU8 negative resist itself have shown a chemical compatibility with Kapton HN. We measured the piezoelectric response on a capacitor test structure: through the Dynamic Mechanical Analyzer we applied controlled forces, and at the same time, by an LCR meter we performed measurements of the capacitance.

EFFECT OF EXTERNAL ELECTRICAL STIMULI ON DNA-BASED BIOPOLYMERS

Biopolymers, such as deoxyribonucleic acid-hexadecyltrimethyl ammonium chloride (DNA-CTMA) and bovine serum albumin-polyvinyl alcohol (BSA-PVA), were studied using a novel capacitive test structure. A variety of external electrical stimuli were applied, including a low frequency alternating current signal and a rf/microwave frequency signal combined with a DC bias. The dynamic responses of the DNA-based biopolymer to the external stimuli are presented in this paper. The electrical transport measurements support the space-charge-limited conduction and the low frequency capacitance–voltage (CV) measurements showed large depletion layer capacitance at the Au –biopolymer interface, at 20 Hz, and the capacitance approaching bulk values at 1 MHz. Electric force microscopy (EFM) was utilized for visualization of charge dynamics and to examine the effect of DC bias combined with an AC signal. Ionic charges in the DNA-CTMA system seem to be responsible for the dynamic response to the various external electrical stimuli.