V. Zieren

A back-wafer contacted silicon-on-glass integrated bipolar process. Part I. The conflict electrical versus thermal isolation

A novel silicon-on-glass integrated bipolar technology is presented. The transfer to glass is performed by gluing and subsequent removal of the bulk silicon to a buried oxide layer. Low-ohmic collector contacts are processed on the back-wafer by implantation and dopant activation by excimer laser annealing. The improved electrical isolation with reduced collector-base capacitance, collector resistance and substrate capacitance, also provide an extremely good thermal isolation. The devices are electrothermally characterized in relationship to different heat-spreader designs by electrical measurement and nematic liquid crystal imaging. Accurate values of the temperature at thermal breakdown and thermal resistance are extracted from current-controlled Gummel plot measurements.

Modeling of light-emission spectra measured on silicon nanometer-scale diode antifuses

Electroluminescence (EL) spectra of nanoscale diodes formed after gate-oxide breakdown of n+-polysilicon/oxide/p+-substrate metal–oxide–semiconductor capacitors were measured in reverse and forward bias. The nanoscale diodes, called diode antifuses, are created by the formation of a small link between the n+-poly and the p+-substrate with the properties of a diode. A previously published multimechanism model for avalanche emission from conventional silicon p–n junctions is applied to fit the EL spectra in reverse-biased silicon-diode antifuses. The results show that the light from reverse-biased diode antifuses is caused by the same phenomena as in conventional p–n junctions. Forward-bias spectra of the diode antifuses show different shapes when lightly or highly doped p substrates are used. In the case of a lightly doped p substrate, the EL intensity in the forward mode is increased by about two orders of magnitude in the visible-wavelength range with a maximum intensity in the infrared region. A phonon-assisted electron–hole recombination model is applied to fit the low-energy part of emitted spectra. The visible emission is attributed to the Fowler–Nordheim tunneling current through the SiO2, enabled presumably by electron capture into SiO2 trap levels and intraband transition of hot electrons injected into the Si bulk.

High bit density (100 Mb/cm/sup 2/) with single-layer Co-Cr media and ring heads in perpendicular magnetic recording

The signal and noise of single-layer Co/sub 79/Cr/sub 21/ media are measured with ring heads to estimate the area density that can be achieved. Densities as high as 100 Mb/cm/sup 2/ (1 mu m/sup 2//bit) are expected when a signal-to-noise ratio sufficient for an error probability less than 10/sup -5/ is required. As a comparison, densities estimated from data from metal-evaporated tape and CrO/sub 2/ tape are given. In the frequency response of the single-layer media, an additional minimum was observed for a wavelength slightly larger than the gap length. This is probably caused by the bipolar nature of the perpendicular recording field of a ring head. >

Magnetostatic and recording analysis of RF-sputtered double layer media for perpendicular recording

The paper describes the preparation, characterization and properties of RF-sputtered double-layer (DL) media for perpendicular magnetic recording. The media, consisting of CoCr on top of a soft magnetic NiFe layer, are deposited on Si wafers or polyester (PET) foils. The influence of an intermediate layer on the magnetic properties such as the NiFe coercivity, is described in terms of magnetostatic (de)coupling. In-contact recording experiments using ring heads include signal as well as noise measurements. Spike noise is observed in low-H c (NiFe) DL media, which probably may be ascribed to domain-wall displacements in the underlayer. The relation between the noise output and H c (NiFe) is shown.

CoCr double‐layered media with NiFe and CoZrNb soft‐magnetic layers (invited)

The magnetic, structural, and recording properties of CoCr double‐layered media are investigated. The underlayer materials NiFe (crystalline) and CoZrNb (amorphous) were combined with two different kinds of intermediate layers: Ti (crystalline) and Ge (amorphous). Applying a bias voltage during sputtering of NiFe results in a low coercivity of the NiFe layer and in a high coercivity of the CoCr layer. The structure of the NiFe layer influences the structure of the CoCr layer. A Ti layer between the NiFe and CoCr layers decreases the in‐plane remanence of the CoCr layer. The coercivity of all CoZrNb layers is low, independent of the application of a bias voltage. The orientation and structure of CoCr on CoZrNb can be improved by using a Ge intermediate layer, which results in a low coercivity of the CoCr. A Ti intermediate layer increases the coercivity. Ring heads show a dependence of spike noise on the underlayer coercivity and on the applied normal force. A probe‐type head shows a dependence of its outp...

Properties of one-sided probe heads on double-layer perpendicular recording media

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.

Efficiency improvement of one-sided probe heads for perpendicular recording on double-layer media

In this paper some improvements are proposed for one-sided probe heads, used for perpendicular recording on double-layer media. Two-dimensional lumped reluctance modelling shows that the read efficiency of the well-known W-shaped single-pole head, or WSP, is very low, but can be improved by more than 10 dB by designing a new triangular coil-chamber geometry. The model also indicates that narrowing the track width with respect to the core width results in a further 5 dB increase in output. Furthermore, a new head design, the V-shaped singIe-pole head (VSP), which shows some distinct advantages with respect to manufacturability, has also been modelled. The experimental results obtained from measurements on VSPs are in good agreement with the model calculations. Despite its somewhat lower efficiency (compared to a WSP with the same triangular coil chamber), this VSP yields > 12 dB output improvement compared to a conventional WSP with a rectangular coil chamber and a wider track.

High performance heads for perpendicular recording

Several important features of past, present and future developments in the field of heads, specifically designed for perpendicular DL (double-layer) media, are outlined. The emphasis is probe heads (PHs) that are positioned on one side of the medium only. The fabrication and measurement of experimental, high-efficiency PHs, the so-called VSPs, are discussed. The experiments indicate that thin Co-Cr layers with a high coercivity are needed for a good short-wavelength response. This imposes several requirements on the pole material, such as a high saturation magnetization, low Barkhausen noise, and high permeability. A playback model is described that enables the head, medium, and interface parameters to be analyzed. The model has also been used to estimate the bit densities that can be obtained with PHs on DL media. An areal density of 1 bit/ mu m/sup 2/ appears feasible. >

Hot-electron degradation in hydrogenated amorphous-silicon-nitride thin-film diodes

Two series of thin-film diodes (TFDs), used as switching elements in active-matrix liquid-crystal displays, have been prepared with various amorphous-silicon-nitride (a-SiNxHy) thicknesses. In a first series, with thin top metal contacts, it was observed by photon-emission spectroscopic analysis that both the effective electron temperature and the number of hot electrons increased as the nitride thickness (at constant field) or the electric field across the TFD (at constant nitride thickness) increased. A further analysis revealed that for the thicker samples, the electrons became progressively hotter on moving from the cathode to the anode. In a second series, the drift of the TFD current–voltage characteristic under dc-driving conditions has been monitored as a function of nitride thickness at various fields. The anodic drift, resulting from defect-state creation in the anodic sample region, and the field and thickness dependence of the hot-electron intensity, show very similar trends. Therefore, it is ...

Light emission from silicon nanometer-scale diode antifuses

Results are presented of the spectrally resolved absolute measurements of the electroluminescence of reverse-biased silicon nanometer-scale diode-antifuses brought into breakdown. The emission spectrum of the diode-antifuses is measured in the energy range of 1.4 - 2.8 eV at different reverse currents. The dependence of the emission intensity on the current was evaluated to study the dominant emission processes. Also the stability of the diode-antifuses has been tested. Results indicate that the diode-antifuse is basically a high quality device. Furthermore due to the nanometer-scale dimensions of the diode-antifuse, very high electrical fields and current densities are possible at low power consumption. This makes the diode-antifuse an excellent candidate to be utilized as a light source in Si- based sensors and actuator applications.