Mao‐Min Chen

Effect of substrate and antiferromagnetic film’s thickness on exchange‐bias field (invited)

In this work, we studied the effect of different substrates and the thickness dependence of the antiferromagnetic layer on the exchange‐bias field, created through interfacial exchange coupling between NiFe and FeMn. The substrates considered were glass and a metallic underlayer, such as Ta, on glass. We noticed different behaviors of the two types of films when annealed in a magnetic field at 240 °C and we carefully looked at their temperature dependence, observing that the blocking temperature, at which the exchange‐bias field goes to zero, decreases with increasing FeMn thickness. We also found that, when reducing the antiferromagnetic film’s thickness, the exchange‐bias field of the annealed NiFe/FeMn structure improves on both types of substrate. Since a low blocking temperature is undesirable, we developed a method to take advantage of the thinner FeMn film’s properties and to compensate the decrease in blocking temperature. The FeMn was deposited in two separate layers. The first layer, at the NiFe...

Silicon doping effects in reactive plasma etching

Silicon etch rates in CF4/O2 plasma have been studied in a diode reactor which allows both reactive ion etching (RIE) and plasma etching. A fluorine population was also measured from the intensity of optical emission in conjunction with argon actinometry, in order to separate etch rates contributed by the ion enhanced etching and the spontaneous chemical etching. A heavily doped n‐type silicon etches faster than undoped silicon, while a heavily doped p‐type silicon etches slower than undoped silicon. Although this doping effect is present in both ion enhanced etching and chemical etching, it is a more severe influence in the isotropic chemical etching. The thermal activation energy for the chemical etching was measured to be 0.10 eV, independent of the chemical and electrical properties of dopants. The Coulomb attraction between uncompensated donors (As+) and chemisorbed halogens (F−) enhances etch rates in a heavily doped n‐type silicon, whereas the Coulomb repulsion between uncompensated acceptors (B−) ...

Silicon etching mechanism and anisotropy in CF4+O2 plasma

From measurements of optical emission and silicon etch rate, we are able to separate contributions due to the chemical etching and the ion‐bombardment enhanced etching in the CF4+O2 reactive ion etching process. The chemical etching part of undoped polysilicon etch rates is linearly proportional to the ground state fluorine population and the ion bombardment part is proportional to the dc self‐bias voltage (V2.3bi). The chemical etching predominates during plasma etching, giving rise to the isotropic etch profile, while both the chemical etching and the ion‐bombardment enhanced etching mechanisms coexist during reactive ion etching. A degree of the etch anisotropy in reactive ion etching is determined by competition between the chemical etching and the ion‐bombardment enhanced etching, and can be expressed by an equation which only involves two physical quantities, etch rate and fluorine concentration, experimentally measurable in plasma etching and reactive ion etching. The silicon loading effect leads t...

Ternary NiFeX as soft biasing film in a magnetoresistive sensor

The properties of NiFeX ternary films (X being Al, Au, Nb, Pd, Pt, Si, and Zr) have been studied for soft‐film biasing of the magnetoresistive (MR) trilayer sensor. In general, the addition of the element X into the NiFe alloy film decreases the saturation magnetization Bs and magnetoresistance coefficient of the film, while increasing the film’s electrical resistivity ρ. One of the desirable properties of a soft film for biasing is high sheet resistance for minimum current flow. A figure of merit Bsρ that takes into account both the rate of increase in Bs and the rate of decrease in ρ when adding X element was derived to compare the effectiveness of various X elements in reducing the current shunting through the soft‐film layer. Using this criterion, NiFeNb and NiFeZr emerge as good soft‐film materials having a maximum sheet resistance relative to the MR layer. Other critical properties such as magnetoresistance coefficient, magnetostriction, coercivity, and anisotropy field were also examined and are di...

Laminated CoZr amorphous thin‐film recording heads

Recording heads with four‐layer laminated CoZr/Ta films as pole pieces have been fabricated using rf sputter deposition and ion milling techniques. Typical 4πMs of 14 000 G were obtained for CoZr amorphous films compared with 10 000 G for Permalloy films. Recording tests performed with this laminated CoZr/Ta film head indicate 8–12 dB better overwrite than with plated Permalloy film heads having an identical structure. However, the former exhibits a 10%–25% lower amplitude than the latter. This may be attributed to the thermal degradation of the initial permeability μi of the CoZr film during head‐fabrication processes. This CoZr/Ta head also shows poorer amplitude stability than the plated Permalloy head.

Doping effects in reactive plasma etching of heavily doped silicon

Etch rates of heavily doped silicon films (n and p type) and undoped polycrystalline silicon film were studied during plasma etching and also during reaction ion etching in a CF4/O2 plasma. The etch rate of undoped Si was lower than the n+‐Si etch rate, but higher than the p+‐Si etch rate, when the rf inductive heating by the eddy current was minimized by using thermal backing to the water‐cooled electrode. This doping effect may be explained by the opposite polarity of the space charge present in the depletion layer of n+‐Si and p+‐Si during reactive plasma etching.

The Effect Of Overcoats On The Ablative Writing Characteristics Of Tellurium Films

The change in the ablative writing sensitivity of Te films due to SiO2 and polymethyl methacrylate overcoats of various thicknesses were measured. These experimental data were compared to results of thermal calculations. We found that thermal losses of the absorbed laser energy to the overcoat layer is usually not negligible even for very thin (≲500 A thick) overcoat layers. In addition to thermal effects which degrade the writing sensitivity of Te films, we found that rigid overcoats combined with rigid substrates can constrain the ablative writing process of Te and hence cause further degradation in the writing sensitivity and in the read‐during‐write signal.

Ablative hole formation process in thin tellurium and tellurium‐alloy films

Static measurement data of contrast ratio versus laser power of single layer Te and Te alloys on polymethylmethacrylate substrates are reported. It is shown that these films can exhibit two regimes of hole formation depending upon laser power. In the lower power regime hole opening must be initiated by voids in the film while for higher powers voids are not necessary for hole opening. This interpretation leads to a better understanding of the hole ablation process as well as some practical consequences.

The microstructure of iron oxide thin films

The microstructural dependence of iron oxide thin films on the film preparation conditions has been systematically evaluated. The main process parameters in this study were substrate temperature, which varied from room temperature to 325 °C, and oxygen flow rate, which was from 3.0 to 9.5 sccm. For the oxygen flow rate below 6.0 sccm during deposition, the crystalline grains are columnar as shown by cross‐section TEM. The columnar structure varied with the deposition temperature. For lower deposition temperature, the columnar diameter is nearly constant across the entire thickness (1000 A) of the film; increasing the temperature tends to increase the diameter of columnar grains along the thickness of the film toward the top surface. It was also noted that the microvoids between columns were present only in the room‐temperature deposited films. These voids are believed due to the shadowing effect, and resulted from the low surface atomic mobility at low deposition temperature. For higher oxygen flow rate (...

Heating effects in reactive etching of Nb and Nb/sub 2/O/sub 5/

The reactive etching mechanism of Nb and Nb/sub 2/O/sub 5/ in CF/sub 4//O/sub 2/ RF plasma has been studied in a flexible diode reactor, with special emphasis on a thin film heating effect. Etch rates of both materials during reactive ion etching are determined by a combination of the ion bombardment enhanced etching mechanism and the chemical etching mechanism. In niobium, the chemical etching always dominates over the ion enhanced etching. Etch rates in the plasma etching mode are primarily due to the chemical etching mechanism. The activation energy in the chemical etching is estimated to be 0.22 and 0.11 eV for Nb and Nb/sub 2/O/sub 5/, respectively. The Nb chemical reactivity (etch rate divided by a number density of the fluorine atoms) shows a substantial increase proportional to RF power and, surprisingly, to Nb film thickness. The thicker the film, the higher the etching rate observed during plasma etching. The authors argue that this is due to a temperature rise in a Nb film caused by the eddy current generated by the RF magnetic field (i.e., the RF inductive heating).