The pedunculopontine nucleus as alternative target for deep brain stimulation

Parkinson’s disease (PD) is a neurodegenerative disease associated with motor and nonmotor symptoms. Deep brain stimulation (DBS) is a surgical treatment where an electrode is implanted in a certain area in the brain. In PD this is mostly done in the subthalamic nucleus (STN) or the globus pallidus interna (GPi). High frequency stimulation (~130 Hz) is often a successful treatment.\ud The pedunculopontine nucleus (PPN) has recently been suggested as a new therapeutic target for DBS, particularly for patients with severe gait and postural impairment [2]. Stimulation at this site is typically delivered at low frequencies in contrast to the high frequency stimulation required for therapeutic benefit in STN [2].\ud Despite real therapeutic successes, the fundamental physiological mechanisms underlying the effect of DBS are still not understood. To get a better understanding of PPN stimulation we construct a computational model for PPN Type I neurons.\u

Squeeze film damping in the free molecular flow regime with full thermal accommodation

We introduce an analytical model for the gas damping of a MEMS resonator in the regime of free molecular flow. Driving force in this model is the change in density in the gap volume due to the amplitude of the oscillating microstructure, which is counteracted by the random walk diffusion in the gap that tries to restore the density to its equilibrium value. This results in a complex-valued force that contributes to both the damping as well as the spring constant, depending on the value of ¿ t with ¿ the resonance frequency and t the random walk diffusion time. The diffusion time is calculated analytically using the model for random walk Brownian motion and numerically by a Monte Carlo simulation of the ballistic trajectories of the molecules following Maxwell-Boltzmann statistics and full thermal accommodation in gas-surface collisions. The model is verified by comparison to accurate data on the pressure dependency of the damping of three MEMS resonators, showing agreement within 10%

Mixed mode bending test for interfacial adhesion in semiconductor applications

Currently, prediction of interface strength is typically done using the critical energy release rate. Interface strength, however, is heavily dependent on mode mixity. Accurately predicting delamination therefore requires a material model that includes the mode dependency of interface strength. A novel test setup is designed which allows mixed mode delamination testing. The setup is a stabilized version of the mixed mode bending test previously described by Reeder and Crews (1990; 1991). It allows for the measurement of stable crack growth over the full range of mode mixities, using a single specimen design. The crack length, necessary for calculation of the energy release rate, is obtained from an analytical model. Crack length and displacement data are used in a finite element model containing a crack tip to calculate the mode mixit

Interfacial adhesion method for semiconductor applications covering the full mode mixity

Currently, prediction of interface strength is typically done using the critical energy release rate. Interface strength, however, is heavily dependent on mode mixity. Accurately predicting delamination therefore requires a material model that includes the mode dependency of interface strength. A novel test setup is designed which allows mixed mode delamination testing. The setup is a stabilized version of the mixed mode bending test previously described by Reeder and Crews (1990, 1991). It allows for the measurement of stable crack growth over the full range of mode mixities, using a single specimen design. The crack length, necessary for calculation of the energy release rate, is obtained from an analytical model. Crack length and displacement data are used in a finite element model containing a crack tip to calculate the mode mixity

Characterization and modelling of moisture driven interface failures

Since moisture sensitivity level (MSL) tests are part ofthe international reliability qualification standards, all the microelectronics components/products have to pass these specifications. Therefore, it is important to be able to efficiently and accurately characterize and predict the moisture related material and interface behaviour in the real manufacturing, processing, testing and application conditions. This paper focuses on our research efforts in and results ofdeveloping and verifYing efficient and accurate characterization and modelling methods for moisture driven interface failures. The methodology incorporates the characterization ofthe strength ofcritical interfaces as function of temperature and humidity using the four-point bending test. Using multi-physics-based Finite Element (FE) models, which take into account both the moisture and thermo-mechanical related failure mechanisms, enables the prediction ofinterface failures. The developed methodology is used for understanding the observed interface failures of an industry carrier

Characterization and modelling of moisture driven interface failures

Since moisture sensitivity level (MSL) tests are part ofthe international reliability qualification standards, all the microelectronics components/products have to pass these specifications. Therefore, it is important to be able to efficiently and accurately characterize and predict the moisture related material and interface behaviour in the real manufacturing, processing, testing and application conditions. This paper focuses on our research efforts in and results ofdeveloping and verifYing efficient and accurate characterization and modelling methods for moisture driven interface failures. The methodology incorporates the characterization ofthe strength ofcritical interfaces as function of temperature and humidity using the four-point bending test. Using multi-physics-based Finite Element (FE) models, which take into account both the moisture and thermo-mechanical related failure mechanisms, enables the prediction ofinterface failures. The developed methodology is used for understanding the observed interface failures of an industry carrier

Delamination prediction in stacked back-end structure underneath bond pads

The thermo-mechanical reliability of integrated circuits (ICs) gains importance due to the reducing feature sizes and the application of new materials. This paper focuses on the delamination in the stacked back-end structure underneath bond pads. Current simulation tools predict this failure mode following a linear elastic fracture mechanics approach; whereas an interface damage mechanics (IDM) approach would be more appropriate to our opinion. The basics of IDM by cohesive zone modeling are outlined. The cohesive zone finite element under consideration is a two-dimensional (2D) linear element for small deformations with an exponential traction separation law. A 2D plane strain model represents a simplified microstructure underneath a bond pad. Several finite element (FE) meshes are constructed with gradually decreasing mesh sizes along the interfaces. Furthermore, two cohesive zone parameter sets are considered, one for 'weak' adhesion between the material layers and one for 'strong' adhesion. The simulations with the FE models demonstrate the capability of IDM to simulate the damage evolution, where several interfacial cracks develop simultaneously. The effect of mesh refinement is illustrated. It improves the convergence of the applied nonlinear solution procedure. Furthermore, the correlation between the adhesion strength and the complexity of the equilibrium path is shown. Finally the conclusions are drawn for the current research and recommendations are given for the further development of IDM applied to delamination prediction in IC back-end structure