Bump Layer Research Articles

Study and fabrication of flexible triboelectric pulse tactile sensor based on laser-induced graphene

In the past, tactile sensors were rigid and difficult to integrate with flexible devices. Recently, flexible triboelectric tactile sensors have attracted widespread attention. The flexibility of these triboelectric tactile sensors makes them suitable for various applications across different fields such as patient monitoring and human-machine interaction. In this study, a flexible triboelectric pulse tactile sensor was proposed and developed. It is constructured from polydimethylsiloxane (PDMS) bump, PDMS spacer and laser-induced graphene (LIG) electrode. The PDMS bump was used as the force conversion structure and the PDMS spacer was used as the fixed end and contact with the PDMS bump layer. The LIG was used as a triboelectric electrode. When an external force is applied to the PDMS bump, the PDMS bump layer makes contact with the LIG electrode and generates triboelectric voltage. Finally, the proposed tactile sensor integrated with a mechanical gripper for fruit grasping was demonstrated.

A novel high-performance trench lateral double-diffused MOSFET with buried oxide bump layer

A shallow-trenched Lateral Double-Diffused MOSFET with folded drift region (FD LDMOS) is proposed in this paper. The new structure divides the drift region into two parts. The left side is introduced in a shallow trench, and the right side is used to take advantage of the buried oxide bump layer. The new structure optimizes the lateral and vertical electric fields simultaneously. The self-adaptation of the drift region improves the doping concentration (Ndd), reducing specific on-resistance (Ron,sp) and parasitic capacitance. The simulation results show that compared with the conventional LDMOS (Con. LDMOS), the breakdown voltage (BV) has increased by 53%, and the figure of merit (FOM) has increased by 173.4%; the power-added efficiency (PAE) near the P3dB operating point is increased from 44.43% to 63.67% at the frequency of 1.2 GHz.

Impact of TSV bump and redistribution layer on crosstalk delay and power loss

The performance of a 3D IC is primarily reliant on the selection of an appropriate bump shape. The most prevalent bump shape (cylindrical) is experiencing substantial stress, power loss and crosstalk issues. TSV bump with a tapered structure have recently attracted considerable attention owing to its low volume fraction and coupling capacitance, that can substantially reduce the stress and crosstalk concerns. An impact of the redistribution layer (RDL), intermetal dielectric and high frequency skin effect are appropriately taken into account for the tapered TSV (T-TSV) with a cylindrical, barrel and tapered bump shape. A mathematical framework of the resistance–inductance–conductance–capacitance (RLGC) structure of the proposed T-TSV have been formulated by effectively considering the coupling, passivation and fringing capacitance of the RDL. In order to benchmark the proposed electrical equivalent circuit, the structural model of the T-TSV is validated against the fabrication based experimental results, and a subsequent analysis have been performed for the stress, crosstalk induced delay, and power loss. The proposed TSV structure is in good agreement with the experimental results with an average deviation of only 2.8%. Furthermore, irrespective of bump height, the tapered bump based T-TSV can effectively reduce the overall crosstalk induced delay, stress, power delay product (PDP), insertion and reflection losses with an average deviation of 20.22%, 22.30%, 23.55%, 8.01%, and 10.32%, respectively, when compared to the barrel and cylindrical bumps. In addition, it has been observed that the overall rate of change in PDP, power losses and crosstalk induced delay with considering RDL are 18.8%, 20.50%, and 25.22%, respectively independent of the bump shapes.

Effect of Bonding Strength on Electromigration Failure in Cu-Cu Bumps.

In microelectronic packaging technology for three-dimensional integrated circuits (3D ICs), Cu-to-Cu direct bonding appears to be the solution to solve the problems of Joule heating and electromigration (EM) in solder microbumps under 10 in diameter. However, EM will occur in Cu–Cu bumps when the current density is over . The surface, grain boundary, and the interface between the Cu and TiW adhesion layer are the three major diffusion paths in EM tests, and which one may lead to early failure is of interest. This study showed that bonding strength affects the outcome. First, if the bonding strength is not strong enough to sustain the thermal mismatch of materials during EM tests, the bonding interface will fracture and lead to an open circuit of early failure. Second, if the bonding strength can sustain the bonding structure, voids will form at the passivation contact area between the Cu–Cu bump and redistribution layer (RDL) due to current crowding. When the void grows along the passivation interface and separates the Cu–Cu bump and RDL, an open circuit can occur, especially when the current density and temperature are severe. Third, under excellent bonding, when the voids at the contact area between the Cu–Cu bump and RDL do not merge together, the EM lifetime can be more than 5000 h.

Mathematical analysis the effect of traffic bump shocking and layer position on the physical properties of Strawberry fruit (Fragaria x ananassa) during transportation

Strawberry is known as a perishable fruit, it is very easy to be damaged as the effect of mechanical force, and this is one of the main problem in postharvest of this fruit. In Indonesia, it is often encountered a traffic bump across the road, this may create a shocking force that may affect the damage of the fruit during transportation. This research was intended to find out the effect of duration of shocking and layer position in the packing box on the physical properties of strawberry fruit. Application of shocking force was done using a special shocking apparatus to the strawberry samples inside wood package box which was arranged in three layers for a certain determined time. After shocking process the sample were then stored at room temperature and continuously monitored. It was found that both the duration of shocking and layer position in the box were significantly affect some of physical properties of the fruit, such as respiration rate, weight loss, brix content, firmness, and lightness of the fruit. The rate of change of physical properties of the fruit could be described appropriately using kinetics model of the zero or first order.

Piezoresistive Polymer Diaphragm Sensor Array Using Conductive Elastomeric Nanocomposite Films for Skin-Mountable Keypad Applications

This paper reports on arrayed piezoresistive polymer diaphragm sensor made entirely of elastomer for skin-mountable keypad applications. Two-step transfer of conductive elastomeric nanocomposites (CENs) combined with soft lithographic techniques enables the achievement of elastic sensing layers with strip-patterned CENs embedded in polydimethylsiloxane (PDMS) channels. After assembling with an elastomeric bump layer, simple all-elastomer sensor architectures are successfully demonstrated. The activated buttons of the sensor can be easily and distinguishably identified by sensing the simultaneous changes in the electrical resistance of CEN strips with respect to the applied force. The straightforward sensing mechanism makes it possible to detect the exact locations of input with negligible crosstalk between adjacent sensing buttons to each other. The usability of the sensor platform as a skin-mountable keypad is also demonstrated by integrating on a wrist. [2014-0072]

Characterization of flip chip bonded structure with Cu ABL power bumps

Power distribution in both 2D and 3D integrated circuit (IC) devices becomes one of the key challenges in device scaling, because the on-chip power dissipation becomes significantly severe and causes thermal reliability issues. In this study, the process solution to resolve the on-chip power dissipation by improving power distribution was investigated through newly designed power bumps called ABL (advanced bump layer) bumps. Rectangular-shaped Cu ABL bumps were fabricated and bonded on Si substrate using flip chip bonding process. The bump height difference in signal and ABL power bumps, bonding interface, and electrical resistivity of flip chip bonded structure were evaluated. The lowest electrical resistivity of Cu ABL bump system was estimated to be 3.3E−8Ωm. The process feasibility of flip chip bonded structure with Cu ABL bumps has been demonstrated.

Fabrication of Advanced Bump Layer for IC Power Delivery

Metal interconnection in the IC technologies is more important than ever for a device performance. A robust power delivery is one of scaling challenges due to increasing operating frequencies, increasing power density, and decreasing supply voltages. Especially, the on-chip power delivery problem becomes much harder as a device scales down due to the lower voltage, higher current density, thinner metal layer, and smaller pad size. The power delivery is in general controlled by minimizing IR drop and controlling circuit noise through circuit designs. However, in this study the newly designed bumps called advanced bump layer (ABL) were evaluated to improve power delivery. The two types of ABL bumps were designed and fabricated by Cu electroplating. Bump height uniformity, surface roughness, plated structure, and sheet resistance were characterized.

OS1805 CuとSn-Ag-Cuはんだから構成されるチップ間接合部の熱伝導特性と力学的変形特性

Equivalent material properties of thermal conductivity, Young's modulus, Shear modulus and Poisson's ratio for micro bump layers were estimated by FEM simulation. The chip connections were built by copper and Sn-Ag-Cu solder and the equivalent material properties showed anisotropy depend on the fine structure of materials in micro bump layer. Response surface of these equivalent material properties were made by using plan of experiment method. Equivalent material properties that are difficult to be derived by the mixing rule can be efficiently derived by using the response surface.

Thermohydrodynamic analysis of bump-type gas foil bearings using bump thermal contact and inlet flow mixing models

Implementation of gas foil bearings (GFBs) in high-temperature applications requires a reliable thermal model that accounts for heat transfers within the rotor−GFB system. The proposed thermohydrodynamic (THD) model takes into account energy transports in air film, heat conductions of shaft, thermal resistance of bump layer, and heat conduction in GFB housing. The model also incorporates analytical models for bump thermal contact and inlet flow mixing to improve the prediction accuracy. Published experimental test data benchmark the THD model predictions. Finally, this paper proposes a new GFB cooling scheme, i.e., supplying a cooling flow radially into the inlet flow mixing zone.

Real-time measurement of the three-axis contact force distribution using a flexible capacitive polymer tactile sensor

In this paper, we report real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS). A unit sensor consists of two thick PDMS layers with embedded copper electrodes, a spacer layer, an insulation layer and a bump layer. There are four capacitors in a unit sensor to decompose a contact force into its normal and shear components. They are separated by a wall-type spacer to improve the mechanical response time. Four capacitors are arranged in a square form. The whole sensor is an 8 × 8 array of unit sensors and each unit sensor responds to forces in all three axes. Measurement results show that the full-scale range of detectable force is around 0–20 mN (250 kPa) for all three axes. The estimated sensitivities of a unit sensor with the current setup are 1.3, 1.2 and 1.2%/mN for the x-, y- and z-axes, respectively. A simple mechanical model has been established to calculate each axial force component from the measured capacitance value. Normal and shear force distribution images are captured from the fabricated sensor using a real-time measurement system. The mechanical response time of a unit sensor has been estimated to be less than 160 ms. The flexibility of the sensor has also been demonstrated by operating the sensor on a curved surface of 4 mm radius of curvature.

Flexible Electronics Sensors for Tactile Multi-Touching

Flexible electronics sensors for tactile applications in multi-touch sensing and large scale manufacturing were designed and fabricated. The sensors are based on polyimide substrates, with thixotropy materials used to print organic resistances and a bump on the top polyimide layer. The gap between the bottom electrode layer and the resistance layer provides a buffer distance to reduce erroneous contact during large bending. Experimental results show that the top membrane with a bump protrusion and a resistance layer had a large deflection and a quick sensitive response. The bump and resistance layer provided a concentrated von Mises stress force and inertial force on the top membrane center. When the top membrane had no bump, it had a transient response delay time and took longer to reach steady-state. For printing thick structures of flexible electronics sensors, diffusion effects and dimensional shrinkages can be improved by using a paste material with a high viscosity. Linear algorithm matrixes with Gaussian elimination and control system scanning were used for multi-touch detection. Flexible electronics sensors were printed with a resistance thickness of about 32 μm and a bump thickness of about 0.2 mm. Feasibility studies show that printing technology is appropriate for large scale manufacturing, producing sensors at a low cost.

Analysis of advanced gas foil bearings with piecewise linear elastic supports

Gas foil bearings (GFBs) rely on their underlying elastic foundation to support radial loads at high rotor speeds. The bump foil strip compliance determines the maximum load capacity with large rotor excursions, well in excess of the bearing nominal clearance. GFBs must be designed properly to permit their reliable (predictable) usage in aircraft engines and other heavy load applications since a too soft elastic foundation results in a bearing with limited load capacity. Configurations in practical use include a second bump strip layer or stop pins underneath the original bumps which become active above a certain load threshold. In these last configurations, the overall stiffness of the support structure has piecewise load versus deflection characteristics. Presently, a simple physical model for GFBs with a double bump strip layer follows. The analysis couples the Reynolds equation for the thin film flow of an ideal gas to the elastic supports deflections. An exact flow advection model is adopted to solve the partial differential equations for the zeroth- and first-order pressure fields, thus rendering the GFB load capacity and frequency-dependent rotordynamic force coefficients. Predictions show that heavily loaded GFBs comprising two bump layers in series and including stop pins prevent too large bump deflections which may induce permanent plastic deformations. The structural damping in a GFB with a two bump strip layer enhances the bearing direct damping force coefficients.

Interfacial delamination and fatigue life estimation of 3D solder bumps in flip-chip packages

Detailed three-dimensional finite element analysis was carried out for area-array solder-bumped flip-chip packages. The analysis enabled determinations of accurate three-dimensional effects on stress distributions as well as local fracture behaviors under thermal load. The 3D analysis also estimated thermal fatigue life of solder bumps. Since dimensions of various components span more than three orders of magnitude, the multi-scale finite element models were utilized to elucidate detailed deformation state near solder bumps. The global–local approach identified of critical solder bumps due to the overall deformation and investigated of interfacial delamination at microstructural level. The local model contained a single solder bump and sub-micron UBM layers. The two-step modeling approach enabled accurate fracture analysis otherwise difficult in large 3D models. Our analysis found the crack driving force and preferred delamination direction based on the 3D J-integral calculations. Shear deformations within and surrounding solder bump connectors were also investigated. The results revealed higher deformation in the 3D model than those predicted from 2D models. Additionally, the strain components were different. This has an important implication on the plastic flow characteristics during cyclic loading. Our model estimated about 25% greater steady-state shear strains in the 3D model than those in the 2D models. This result suggests a much shorter fatigue life than that based on the 2D analysis.