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Gate Oxide

4200-SCS Software
4200-SCS software enables you to quickly configure linear or custom C-V, C-f and C-t sweeps with up to 4096 data points. Built-in parameter extraction examples, test libraries and sample programs allow you to easily extract common measurement parameters such as oxide thickness, flat-band voltage, doping concentration etc. With Keithley built-in Confidence Check diagnostic tool, you can check the integrity of open and short connections and connections to your DUT.

Oxide Thickness
The oxide capacitance (COX) is the high frequency capacitance when the device is biased for strong accumulation. In the strong accumulation region, the MOSFET acts like a parallel-plate capacitor and the oxide thickness (TOX) may be calculated from (COX) and the gate area. The 4200-SCS easily extracts these parameters from C-V measurements and displays the results.

Flatband Voltage & Capacitance
Application of a certain gate voltage, the flatband voltage (VFB), results in the disappearance of band bending. At this point, known as the flatband condition, the semiconductor band is said to become flat. Flatband voltage and its shift are widely used to extract other device parameters, such as oxide charges. One method to determine VFB is to use the flatband capacitance method. The ideal value of the flatband capacitance (CFB) is calculated from the oxide capacitance and the Debye length. Once the value of CFB is known, the value of VFB can be obtained from the C V curve data. These parameters are quickly derived and displayed using the user-modifiable projects included with the 4200-SCS parameter analyzer.

Threshold Voltage
The turn-on region for a MOSFET corresponds to the inversion region on its C V plot. When a MOSFET is turned on, the channel formed corresponds to strong generation of inversion charges. It is these inversion charges that conduct current. The threshold voltage (VTH) is the point on the 
C V curve where the surface potential (ÏS) equals twice the bulk potential (ÏB). This curve point corresponds to the onset of strong inversion. For an enhancement-mode MOSFET, VTH corresponds to the point where the device begins to conduct. The VTH parameter is quickly derived and displayed using the user-modifiable projects included with the 4200-SCS parameter analyzer.

Bulk Oxide Charge
The effective oxide charge (QEFF) represents the sum of oxide fixed charge (QF), mobile ionic charge (QM), and oxide trapped charge (QOT): QEFF = QF + QM + QOT

Simple measurements of oxide charge using C V measurements do not distinguish the three components of QEFF. These three components can be distinguished from one another by temperature cycling.

Doping concentration
The doping profile of the device is derived from the C V curve based on the definition of the differential capacitance as the differential change in depletion region charges produced by a differential change in gate voltage. The CVU_MOScap project included in the 4200-SCS computes the depletion depth (w) from the high frequency capacitance and oxide capaci-tance at each measured value of the gate voltage (VG). Once the doping concentration and depletion depth are derived, the 4200-SCS plots the doping profile.

Mobile Ions
The C-V method is one of the more common ways to measure mobile ion concentration. The first step is to measure a high-frequency C-V curve on a MOS capacitor fabricated on the sample wafer. After this measurement, a bias voltage is applied to the MOS capacitor, and the wafer is heated to increase the mobility of the mobile ions. In typical tests, the bias voltage is selected to cause a 106 V/cm field in the oxide with a temperature between 200° â300° C. The wafer is held at these voltage and temperature conditions for a few minutes. After the sample is returned to 23° C , the bias voltage is removed, and another C-V measurement is taken. By comparing the flatband voltage before and after the stress, the mobile ion concentration can be calculated.

4200-SCS Parameter Analyzer Mainframe
The 4200-SCS is a modular, fully integrated parameter analyzer that performs electrical characterization of devices, materials or processes. With nine measurement slots and a built-in low noise ground unit, you can configure it to precisely meet your test requirements or budget constraint.

SMU Modules
SMUs are precision instruments which are used for sourcing current or voltage and simultaneously measuring current and voltage with high accuracy and speed.
Two SMU models are available for use with the 4200-SCS, the 4200-SMU medium power SMU or 4210-SMU high power SMU. Both models occupy only one instrument slot and up to a total of nine can be installed in the 4200-SCS.

Offering the industryâs widest dynamic range, the medium power 4200-SMU operates from 100 nA to 100 mA and 1 uV to 210 V and the high power 4210-SMU operates up to 1 A. The low current measurement capabilities of either SMU can be extended to 0.1 fA resolution by adding an optional preamplifier.

Preamplifier Unit
The low current measurement capabilities of any SMU can be extended to 0.1 fA by adding an optional preamplifier. The 4200-PA can be mounted on the back of the 4200-SCS or in a remote location such as the prober platen or light-tight enclosure to eliminate problems due to long cables.

C-V Module
The 4200-SCS can be configured to support multi-frequency (1 kHz to 10 MHz) C-V, Very Low Frequency (10 mHz – 10 Hz) C-V, and Quasi-static C-V measurements.

The 4210-CVU multi-frequency C-V module occupies one slot in the 4200-SCS chassis and provides C-V, C-t, and C-f measurement sweeps with up to 4096 data points. Built-in compensation routines remove parasitic effects and ensures the integrity of connections to the DUT. An optional power package allows a DC voltage bias of up to +/- 200 V.

The Very Low Frequency C-V method takes advantage of the low current measurement capability of the 4200-SCS Source Measure units (SMUs) to perform C-V measurements. The Very Low Frequency C-V technique makes it possible to measure very small capacitances at a precise low test frequency. This patent-pending, narrow-band sinusoidal technique allows for low frequency C-V measurements of very high impedance devices, up to >1E15 ohms.

Quasi-static C-V employs a DC measurement technique using two 4200-SCS Source Measure Units (SMUs) with two 4200-PA preamplifiers. The SMUs are used to source a current to charge the capacitor, and then to measure the voltage, time and discharge current. The 4200-SCS software includes test programs and formulas to extract common C-V parameters.

Probe Station
The 4200-SCS can control external equipment such as an automated or semi-automated probe stations, temperature controllers etc. Probe drivers are supplied with the 4200-SCS for select Cascade Microtech, Suss, MicroManipulator and Signatone probe stations.

Device Under Test (DUT)
The 4200-SCS is capable of testing many devices or materials: