Örjan Vallin

Quartz‐to‐Quartz Direct Bonding

Direct bonding of single crystalline quartz wafers is presented. By this straightforward technique, hermetical seals between quartz wafers can be formed. Nearly Z-cut (the Z-cut rotated 1 degrees 5 ...

Inversion in Metal–Oxide–Semiconductor Capacitors on Boron-Doped Diamond

For the advancement of diamond-based electronic devices, the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial, as this device finds applications in numerous fields of power electronics and high-frequency systems. The MOS capacitor forms the basic building block of the MOSFET. In this letter, we describe planar MOS capacitor structures fabricated with atomic layer deposited aluminum oxide as the dielectric on oxygen-terminated boron-doped diamond substrates with different doping levels. Using capacitance-voltage measurements, we have, for the first time, observed inversion behavior in MOS structures on boron-doped diamond, with a doping concentration of 4.1 × 1019/cm3.

Novel Silicon-on-SiC Substrate with Superior Thermal and RF Performance

A novel Si-on-SiC hybrid substrate is demonstrated using MOSFET devices. This is the first demonstration ever of this technology, to the best knowledge of the authors. The direct bonded substrate uses polysilicon as an intermediate layer, thereby eluding the thermally unfavourable SiO2. The MOSFET characteristics as well as the absence of self-heating effects are shown and are benchmarked against devices on commercially available epitaxial and SOI wafers, as well as Si-on-poly -SiC (SoPSiC, PicoGiga). Previous efforts to improve the thermal properties by replacing the SiO2 insulator have included diamond, AIN, and Al2O3.

High-temperature piezoresistive gauge fabricated on commercially available silicon-on-insulator wafers

This paper presents a four-terminal piezoresistive gauge intended for use at high temperatures. The gauge has proven to operate at temperatures as high as 400 °C. Calibrated measurement of forces ranging from 0 to 40 mN has been conducted at temperatures up to 300 °C. The device is manufactured in a straight-forward process from commercially available bonded silicon on insulator (SOI) wafers. The temperature dependence is minimized as the piezoresistor is electrically insulated from the substrate, it is small in size, and it makes good use of the shear modulus of piezoresistivity.

Buried aluminum nitride insulator for improving thermal conduction in SOI

A new Si-on-AlN substrate has been fabricated and characterised both electrically and thermally. Thermal properties of the new substrate have been identified with a thermal resistance reduced by half to 47.5 K/W compared to reference SOI. Further improvements in fabrication of these new SOI substrates with regard to the alpha-Si layer, oxide layer and in AlN film quality itself would utillise the thermal conductivity of AlN even more.

Direct bonded quartz resonators

In contrast to other methods direct bonding allows for the joining of two materials without an intermediate layer as in soldering or gluing. Although often putting tremendous requirements on the surfaces to be joined in terms of cleanliness and smoothness - direct bonding generally provides extraordinary adhesion and stability. In the semiconductor industry the direct bonding of silicon has been successfully employed for many years. Recently we showed that the technology, with some modifications, could be applied also to single crystalline quartz, and that the direct bonding of quartz could be achieved with arbitrary cuts and in various directions. The ability to unite quartz wafers ultimately enables new resonator, filter, and sensor concepts, and the ability to bond pre-processed wafers make true all-quartz packages possible. In present work, we investigate the influence on a resonator by including a direct bonded interface.

Silicon fusion bond interfaces resilient to wet anisotropic etchants

The bond interface in silicon microsystems is sensitive to the subjection to wet anisotropic etchants. Fusion bond interfaces of bonded wafers resilient to potassium hydroxide or tetramethyl ammonium hydroxide etching are obtained using wafers of oxidized silicon bonded to oxidized silicon, where the bond oxide is removed by trifluoromethane plasma etching. Other investigated bond configurations initiate severe damages during etching.

LDMOS transistors on Si-on-SiC hybrid substrates having crystalline or poly-crystalline SiC - electrical and thermal characterization

First ever demonstration of LDMOS transistors on Sion-SiC hybrid substrates. No degradation in transistor performance as compared to conventional SOI. Poly-SiC is available in larger wafer sizes but seems to have slightly lower heat conductivity than crystalline SiC. The intermediate a-Si layer provides electrical advantages and does not form any thermal barriers.

Polishing of Quartz by Rapid Etching in Ammonium Bifluoride

The etch rate and surface roughness of polished and lapped AT-cut quartz subjected to hot (90, 110, and 130degC), concentrated (50, 65, 80 wt%) ammonium bifluoride have been investigated. Having used principal component analysis to verify experimental solidity and analyze data, we claim with confidence that this parameter space does not, as elsewhere stated, allow for a polishing effect or even a preserving setting. Etch rates were found to correlate well, and possibly logarithmically, with temperature except for the hottest etching applied to lapped material. Roughness as a function of temperature and concentration behaved well for the lapped material, but lacked systematic variation in the case of the polished material. At the lowest temperature, concentration had no effect on etch rate or roughness. Future efforts are targeted at temperatures and concentrations closer to the solubility limit.

Morphological instability of Ag films caused by phase transition in the underlying Ta barrier layer

Wide-bandgap (WBG) semiconductor technologies are maturing and may provide increased device performance in many fields of applications, such as high-temperature electronics. However, there are still issues regarding the stability and reliability of WBG devices. Of particular importance is the high-temperature stability of interconnects for electronic systems based on WBG-semiconductors. For metallization without proper encapsulation, morphological degradation can occur at elevated temperatures. Sandwiching Ag films between Ta and/or TaN layers in this study is found to be electrically and morphologically stabilize the Ag metallization up to 800 °C, compared to 600 °C for uncapped films. However, the barrier layer plays a key role and TaN is found to be superior to Ta, resulting in the best achieved stability, whereas the difference between Ta and TaN caps is negligible. The β-to-α phase transition in the underlying Ta barrier layer is identified as the major cause responsible for the morphological instabi...