Gate area

Note that both the insulated runner and the distribution tube systems rely on a cartridge heater in the gate area to prevent premature freezing off at the gate (see Fig. 4.40). 

We choose the ratio between the gate area and the discharge opening area,... 

The product designer should caution the tool designer to keep the gate area away from load-bearing surfaces and to make the gate size such that it will improve the quality of the product. It so happens that the product wall in the gate area develops the minimum tolerance due to the high melt pressure in that area. 

There is not too much orientation that is permanently added to material as it passes through the gate since the continued flow in the cavity basically tends to produce turbulence that destroys the orientation. The last material to pass through, however, does retain its orientation and the gate area in a molded product is usually highly oriented and could be weak. In the case of jetting, the result is a patch of highly oriented material somewhere on the molded product near where the first material entered the mold. 

In pulse-power applications, the thyristor is required to supply energy to the load in a very short period of time, which requires that it provide extremely high-current slew rates. During turn-on, excess carrier density increases near the gate area and then spreads throughout the device. As the excess carriers spread, the anode-to-... 

Successful operation of potentiometric chemosensors opened up the possibility for the fabrication of chemical field-effect transistors (chemFETs) and ion-selective field-effect transistors (ISFETs). A sensing element in these devices, i.e. the MIP film loaded with the molecular, neutral or ionic, respectively, imprinted substance is used to modify surface of the transistor gate area. Apparently, any change in the potential of the film due to its interactions with the analyte alters the current flowing between the source and drain. 

The ISFET transducer, described in a previous paper (2), is an n-Si, p-well type device with the sensitive gate consisting of a thermally deposited SiC>2 (1000 A) and an APCVD deposited AI2O3 (600 A) layers. The gate area is 20 pm x 500 pm and the overall chip dimensions are 0.75 mm x 3 mm x 0.38 mm. 

The drain-source capacitance Qs can be neglected since only a constant drain voltage Vis is applied. The total gate capacitance is given by Cg = tot Q with yf tot ihs total gate area. The unity-gain bandwidth can now be calculated from Eqs. (8), (10) and (12) ... 

Pressures above 15 MPa help fill the mold before its components such as the mandrel and casings begin to cool. Above 25 MPa melt pressure, the mold part may crack at the gate. The equipment should allow control of transfer rate and transfer pressure. Once the filling is nearly complete (90%-95%), the transfer pressure should be lowered to half to two-thirds of its initial value to avoid stress concentration in the gate area. The pressure profile has to maximize hold pressure (Fig. 6.57) for packing without crack formation at the gate. 

Electrolyte concentration Channel Gate area length/width ON/OFF Switch speed Switch speed (ON = OFF)a... 

Additional photolithographic steps similar to those discussed earlier are necessary to reopen the silicon dioxide covering source and drain areas above the p-type regions and to create a very thin silicon-dioxide layer below the gate area. The next step involves deposition of a metal such as aluminum to form the contacts for the source, gate and drain. Finally, an interconnection pattern is defined to connect the transistor with other electrical components on the surface. The transistors are now finished and the wafers proceed to other processing operations. 

Sometimes, there are imperfections due either to crystallinity in the preform or due to crystallinity allowed to form during the reheat process. These imperfections show up as haze (pearlescence). This is due to microcracks in the PET induced by the stresses during blowing. This is different from the white color around the gate area of the preform, which is due to thermal crystallization. 

Figure 5.3 shows the drain current of PEI/starch functionalized HEMT sensors measured exposed to different CO2 concentration ambients. The measurements were conducted at 108°C and a fixed source-drain bias voltage of 0.5 V. The current increased with the introduction of CO2 gas. This was due to the increase in net positive charges on the gate area, thus inducing electrons in the 2DEG channel. The response to CO2 gas has a wide dynamic range from 0.9% to 40%, as shown in Fig. 5.4. Higher CO2 concentrations were not tested because there is little interest in these for medical-related applications. The response times were in the order of 100 s. The signal decay time was slower than the rise time, and was due to the longer time required to purge CO2 from the test chamber.

The channels through which the plasticized material enters the gate areas of the mold cavities are called runners. Normally, runners are either hill round or trapezoidal in cross section. Round cross section offers the least resistance to the flow of material but requires a duplicate machining operation in the mold, since both plates must be cut at the parting line. In three-plate mold designs, however, trapezoidal runners are preferred, since sliding movements are required across the parting-Hne ruimer face. 

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