08.06.2014
Semiconductor Today : the first choice for professionals who demand timely, focused, top-quality coverage of the compound semiconductor industry. The wafer bonding market is a very complex one spanning not only different applications but also different wafer sizes (from 2a€™a€™ to 12a€™a€™) and different bonding technologies (adhesive, anodic, fusion, direct oxide, eutectic, glass frit, metal diffusion).
Wafer bonding is usually defined as a process that temporarily or permanently joins two wafers or substrates using a suitable process.
For CMOS image sensors, the advent of back-side illumination technology has raised the competition between molecular bonding and adhesive bonding. Although EV Group is the market leader in permanent bonding, growth of the bonding equipment market is attracting challengers, notes Yole. Disclaimer: Material published within Semiconductor Today and related media does not necessarily reflect the views of the publisher or staff.
Wafer bonding is usually defined as a process that temporarily or permanently joins two wafers or substrates using a suitable process. Besides MEMS and CIS manufacturing, wafer bonding also can be used for LED and power device fab.
Over the 5 past years, much attention has been given to wafer bonding for 3D integration of memories, for example, and other die.
Although EV Group (EVG) is the market leader in permanent bonding, the growth of the bonding equipment market is attracting challengers. A novel structure of the resonant pressure sensor is presented in this paper, which tactfully employs intercoupling between dual pressure-sensing diaphragms and a laterally driven resonant strain gauge. Figure 3a is the displacement finite element (FE) which results when pressure loads on the diaphragms, and the results indicate that there is almost no out-of-plane displacement in the resonator when pressure creates deflection of the diaphragms and silicon islands. FOTURAN® II is a technical glass that crystallizes after UV exposure and temperature processes. Structured FOTURAN® II substrates can be applied in the semiconductor chip and semiconductor packaging processes. Indeed, in a typical LED active regions, spontaneous emission scatters photons in all directions. Metal direct bonding also gives good hermeticity and mechanical stability for many MEMS applications.
Growth will be driven by small size wafers for LEDs and 12a€? wafers for 3D stacking and CIS. The growth will be driven small-size wafers for LEDs and 12" wafers for 3D die stacking and CIS. Historically developed for MEMS and then SOI wafers, wafer bonding technology has shifted to non-mainstream IC applications over the last years. Up to two different wafer bonding steps can be necessary for next-generation CMOS image sensor fab: one for back-side illumination, the second for wafer-level chipscale packaging (WLCSP). It gives 2010-2016 market forecasts for permanent bonding, equipment, an overview of the different bonding approaches and equipment players market shares and competitive information, This market & technology report also presents the trends for permanent bonding, wafer-to-wafer (W2W) vs. After the resonant pressure sensor principle is introduced, the coupling mechanism of the diaphragms and resonator is analyzed and the frequency equation of the resonator based on the triangle geometry theory is developed for this new coupling structure.
IntroductionThe resonant pressure sensor, which is one of the typical microelectromechanical systems (MEMS) devices, has been successfully applied in aerospace, industry control, and instrument calibration due to its highly accurate frequency output.
The blue body represents pressure-sensing layer with dual symmetrical diaphragms, the yellow body represents resonator layer, and the green body represents vacuum cap layer. Coupling Mechanical Mechanism between Diaphragms and ResonatorThe structure definition must be clear before theory calculation.
FE simulation results about the roles of the release beams, support beams, and stable beams are shown in Figure 3b, displacement data on the bottom face of the pressed beam is obtained, and the results indicate that the support beams play the most important role in preventing the resonator from being deflected out-of-plane by the applied pressure even with the two diaphragms.


The crystallized areas can be etched away with a high aspect ratio, resulting in extremely fine structures and vias.
The process flow works without photo resist and can be used with standard semiconductor equipment.
If the substrate material has a smaller band gap than the active region, about half of the light is absorbed in the substrate, significantly reducing device performance. For example, the Nasiri fabrication process uses eutectic bonding of the MEMS directly on the aluminium layer of the CMOS wafer. The report aims at analyzing the market perspectives and technical trends for permanent bonding. Metal direct bonding also provides hermeticity and mechanical stability for many MEMS applications. For CIS, the advent of backside illumination (BSI) technology has raised a competition between molecular bonding and adhesive bonding. If the substrate material has a smaller band gap than the active region, approximately half of the light is absorbed in the substrate; significantly reducing device performance.
Used as accelerometers, pressure sensors, optical devices, microfluidic devices, and more, these microfabricated sensors and actuators often need to be exposed to the environment, but also need to be protected from environmental factors.
The finite element (FE) simulation results match the theoretical analysis over the full scale of the device.
In the past 30 years, several different structures of resonant pressure sensors with different excitation and detection types have been developed [1,2,3,4,5,6].
Figure 2 shows a schematic of the silicon resonator and force transmission from the symmetrical dual diaphragms to the resonator, and the dual diaphragms are marked for clear view. The malposition between the movable combs and the fixed combs is decreased about an order of magnitude in an ANSYS software simulation when the release beams, support beams, and stable beams are added.The sensor is calculated in two parts, as described at the end of the first paragraph in Section 2. After a second exposure and tempering process, the glass can be transformed into a glass ceramic. So, one of the manufacturing solutions for photon loss involves bonding a wafer containing an array of devices to another wafer that provides both a reflective surface for maximum light extraction and a heat sink for thermal management. For example, Nasiri uses eutectic bonding of the MEMS directly on the aluminum layer of the CMOS wafer.
So, one of the manufacturing solutions for photon loss involves bonding a wafer containing an array of devices to another wafer that provides both a reflective surface for maximum light extraction and a heatsink for thermal management.
Industry experts will examine the potential for the semiconductor factory of the future, and discuss potential roadblocks. As seen in Figure 2a, the resonator, which is suspended above the substrate by support beams, consists of combs and the resonant mass, pressed beam, and stable beams.
In the operation of the sensor, axial displacement ?x of the connect beams is the link of the two parts, and ?x is also the horizontal displacement of the force transmission of the silicon island.
Obviously, the scale factor (rate of change of the frequency of the working mode with respect to the pressure load) is not easily calculated, so the mathematic software mathematica 4.0 is used to solve the frequency function of the pressure with different structure parameters.
Also, of course, over the five past years much attention has been given to this technology for 3D integration of memories, for example. STMicroelectronicsa€™ latest three-axis accelerometer (LIS3DH) also shows a different sealing technique compared to what is usually used: gold eutectic sealing allows a dramatic die size reduction. The coupling structure has a simpler structure function partition, which can easily be divided into two connected parts: the pressure-sensing element and the pressure transition element.
The pressed beam and stable beams are the main resonant structures, and the stable beams increase the torsional stiffness and stability of the resonant beams.
To quantifiably analyze the effect of the diaphragms and silicon islands on the range and sensitivity of the sensor, the mechanical model is set in Figure 3c and theoretical derivation follows.


Since 1998 he is a co-founder of Yole Développement, a market research company based in France. As is well known, a diaphragm, which has been widely used in capacitive and piezoresistive pressure sensors, is the most common sensing element. On one side of the fixed combs is the driven electrode and on the other side is the sensing electrode for the frequency readout, the vibration direction is seen along the blue arrow hollow, as shown in Figure 2a. Compared with the thinner pressure-sensing diaphragms, the strong silicon island can be regarded as a rigid body. A resonator with a high quality factor (Q-factor) [7], whose resonant frequency is changed with the beam internal stress, is used as a pressure transition element.A critical design element for a MEMS pressure sensor is to maximize the conversion from the pressure-induced diaphragm strain to the resonator strain while maintaining minimal un-wanted mechanical coupling between the diaphragm and the resonator with a limited design size, which define the sensor size, Q-factor, pressure full-scale range, linearity, and frequency stability. Two ends of the pressed beam are connected to the silicon islands attached to the diaphragms by connect beams and release beams, and all of the beams are suspended, as shown in Figure 2b. The size of each diaphragm is 1500 ?m ? 3000 ?m and silicon islands are located along the long side of the diaphragms, as seen in Figure 2.
Several structures have been tried to minimize the mechanical coupling between the diaphragm and the resonator. The structure in the internal area of the dash-dot line (Figure 2a) is vacuum-packaged with a glass cap as seen in Figure 1, so the resonator vibrates with low air damping for a high Q-factor. The island is deemed to rotate about the long side line when pressure is loaded, as seen in Figure 3c, since the big diaphragm has a tiny deformation [17]. Yole Développement is a group of companies providing market research, technology analysis, strategy consulting, media in addition to finance services. One of the most effective structures is that the direction of the fundamental resonant modes of the diagram and the resonator are perpendicular [8,9,10,11].
External pressure leads to diaphragm deflection, and press stress, induced by diaphragm deflection, is applied on the ends of the pressed beam via the connect beams and release beams. Generally, the deflection direction of the diaphragm is in the out-of-plane and the vibration direction of the resonator is in the in-plane.
However, the deflection of the diaphragm can make the resonant beam shift and bend in the out-of-plane direction if the resonator is placed on the same diaphragm as the pressured-induced diaphragm [1,8,12].
Therefore, the resonant frequency of the resonator could be changed by the external pressure.
In this way, the converted strain from the diaphragm to the resonator is not pure axial beam stress.
For the capacitive sensing resonator, this phenomenon would cause the capacitance change not only in the in-plane direction but also in the out-of-plane direction. The in-plane capacitance change is employed for the resonant mode, while the pressured-induced out-of-plane capacitance change will lead to the phase shift in the self-exciting oscillation circuit. As a consequence, the out-of-plane capacitance change will introduce phase noise in the circuit and reduce the measuring range of the sensor. When the phase shift exceeds the self-oscillation phase range, the circuit will freeze the oscillator.In this paper, a pressure sensor with dual diaphragms and combined beams to achieve a purer structure function partition and reduce the unnecessary coupling between the diaphragms and the resonator is presented. Structure design, finite element simulation, fabrication, and test results are included in this paper.



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