Embedded cooling with 3D manifold for vehicle power electronics application: Single-phase thermal-fluid performance

This work presents a survey of computational methods for adhesive contact focusing on general continuum mechanical models for attractive interactions between solids that are suitable for describing bonding and debonding of arbitrary bodies. The most general approaches are local models that can be applied irrespective of the geometry of the bodies. Two cases can be distinguished: local material models governing the constitutive behavior of adhesives, and local interface models governing adhesion and cohesion at interfaces in the form of traction–separation laws. For both models various sub-categories are identified and described, and used to organize the available literature that has contributed to their advancement. Due to their popularity and importance, this survey also gives an overview of effective adhesion models that have been formulated to characterize the global behavior of specific adhesion problems.

A Survey of Computational Models for Adhesion

This paper reports a dual-contact microelectromechanical switch, which consists of two contacts in a single switch: one with a soft contact material and the other with a hard contact material to achieve low contact resistance and high reliability at the same time under hot switching conditions. In a single switching operation, the proposed dual-contact switch makes contact twice in sequence, where the first contact is made with a hard contact material (Pt-to-Pt) that can withstand an abrupt hot switching condition (high electric field or micro-arcing). The second contact is then accomplished with the soft contact material (Au-to-Au) that has low-contact resistance, through which most of the current flows. In contrast, when the switch releases contact, the Au-to-Au contact is initially detached, and this is followed by the release of the Pt-to-Pt contact. In this way, the dual-contact switch showed longer lifetime than that of a single Au-to-Au contact-only switch by up to fortyfold, and even better lifetime than that of a single Pt-to-Pt contact-only switch by more than two times in open laboratory environments (unpackaged). At the same time, contact resistance of the dual-contact switch was under 0.3 Ω at 50 V of the gate voltage, which is more than seven times smaller than that of the single Pt-to-Pt contact-only switch (2.2 Ω), due to the Au-to-Au contact sub-switch (the contact resistance of the single Au-to-Au contact-only switch was 2.2 Ω).

Complementary Dual-Contact Switch Using Soft and Hard Contact Materials for Achieving Low Contact Resistance and High Reliability Simultaneously

New microstructures for the measurement of the interfacial adhesion force between polycrystalline silicon surfaces in micro- and nanoelectromechanical systems and at elevated temperatures are introduced. The devices consist of bilayer cantilever beams with different coefficients of thermal expansion, which carry a rigid plate with a dimple as one of the contacting surfaces. A landing pad patterned on the substrate serves as the second contact surface. Thermal actuation and structural force stored in the beams initiate and terminate, respectively, the contact between the dimple and the landing pad. The presented designs eliminate the effect of the electrostatic force caused by trapped charges at the contact surfaces and drastically reduce the capillary force caused by ambient humidity, both of which may contribute to the adhesion forces measured by other techniques. This allows us to separately measure different sources of adhesion force. The measurement results show that in the absence of electrostatic and capillary forces, the value of the adhesion force is notably reduced and is independent of contact area over the examined range.

Characterization of Adhesion Force in MEMS at High Temperature Using Thermally Actuated Microstructures

Nowadays, electronics face a challenge regarding the power consumption of integrated circuits (ICs). There is a need for new devices that can provide improved switching capabilities. The downscaled electrostatically actuated ohmic switch, as a (re)emerging device, is a promising candidate to meet this need. To bring such a device seamlessly into IC design, it must be accompanied by an accurate, fast and robust analytical compact model. The development and the main characteristics of such a model are described within this paper. Extensive numerical simulations and measurements have been used to validate the model.

Analytical Compact Model in Verilog-A for Electrostatically Actuated Ohmic Switches

An electrostatically actuated double-clamped beam test structure has been designed and fabricated for the quantitative determination of adhesion forces between two contacting polycrystalline silicon (polysilicon) surfaces. The experimental measurements of the beam profile at varied bias and simulations based on finite element methods are combined to evaluate more accurately the adhesion forces experienced between polysilicon surfaces. In particular, the electrostatic force at pull-off is obtained by measuring the pull-off voltage and the beam profile through optical interferometric methods. The adhesion force is then determined from the mechanical restoring force obtained by finite element methods simulations and the calculated electrostatic force. The results show a weak scaling of the adhesion force with the apparent contact area, defined via microfabricated dimples.

https://iopscience.iop.org/article/10.1088/0960-1317/20/9/095015/pdf

Measurement of adhesion forces between polycrystalline silicon surfaces via a MEMS double-clamped beam test structure

This paper reports on accurate analysis of adhesion force between polysilicon–polysilicon surfaces in micro-/nanoelectromechanical systems (M/NEMS). The measurement is carried out using double-clamped beams. Electrostatic actuation and structural restoring force are exploited to respectively initiate and terminate the contact between the two surfaces under investigation. The adhesion force is obtained by balancing the electrostatic and mechanical forces acting on the beam just before the separation of the two surfaces. Different finite element models are developed to simulate the coupled-field multiphysics problem. The effects of fringing field in the electrostatic domain and geometric nonlinearity and residual stress in the structural domain are taken into consideration. Moreover, the beam stiffness is directly obtained for the case of combined loading (electrostatic and adhesion). Therefore, the overall electrostatic and structural forces used to extract the actual adhesion force from measured data are determined with high accuracy leading to accurate values for the adhesion force. The finite element simulations presented in this paper are not limited to adhesion force measurement and can be used to design or characterize electrostatically actuated devices such as MEM tunable capacitors and micromirrors, RF switches and M/NEM relays.

https://iopscience.iop.org/article/10.1088/0960-1317/21/11/115025/pdf

A finite element technique for accurate determination of interfacial adhesion force in MEMS using electrostatic actuation

A new structure for the measurement of interfacial adhesion force between polycrystalline silicon (polysilicon) surfaces in M/NEMS and at elevated temperature is introduced. The device consists of bilayer cantilever beams with different coefficients of thermal expansion (CTE), which carry a rigid plate with a dimple. Thermal actuation and structural force stored in the beam, respectively, initiate and terminate the contact between the two surfaces under study. The proposed design can eliminate the effect of secondary forces such as electrostatic force caused by trapped charges at contact surfaces, which may contribute to the adhesion forces measured using other techniques.

G H Li

Papers

Measurement of adhesion forces between polycrystalline silicon surfaces via a MEMS double-clamped beam test structure

A finite element technique for accurate determination of interfacial adhesion force in MEMS using electrostatic actuation

Measurement of adhesion force at elevated temperatures in MEMS using thermal-structural actuation