Flicker Noise Measurement and SPICE Parameter Extraction for Modeling and Characterization Service

 

Part 2

 

Introduction

Flicker Noise (or 1/f noise) is the dominant noise source in MOSFET devices at low frequencies. In the carrier-density fluctuation model, the mechanism of Flicker Noise is described as the random capture and emission of electrons by oxide interface traps. The mobility fluctuation model explains the noise source as the carrier mobility fluctuations. Both models agree that the 1/f noise is the fluctuation in the conductivity. At detailed description of the models can be found in the November 1996 issue of the Simulation Standard.

Flicker Noise characteristics are technology (process) and bias dependent. Noise characteristics should be re-characterized with every process change, and should be monitored as a routine process control. For circuit design applications, flicker noise should be modeled over full bias range of VDS, VGS and VBS voltages.

Flicker noise measurement and modeling was first introduced in UTMOST II as an integrated solution in late 1989. At the same time high frequency noise modeling using the HP 8970 was also introduced.

Measurement

The instruments recommended for setting up a cost effective measurement environment are a HP 3561 Dynamic Signal Analyzer for measuring the spectral density and a HP 4145, HP 4141, or HP 4155/56 DC analyzer. Since the device noise level is sometimes below the instrument's measurement capability, Silvaco has developed a custom, cost effective low noise amplifier. Care should be exercised when connecting the DUT and the amplifier box. Connecting cables should be at least double shielded co-axial cables. The cables will protect the signal integrity from undesired interference of CRT monitors, computer CPUs and other measurement instruments.

Automatic I-V and 1/f noise measurements can be performed on wafer level or on packaged devices. There is no limitation on the number of DC bias points that can be specified.

A typical measured spectral density versus frequency curve is shown in Figure 1. On this plot, the bias conditions, slope and intercept of the linear least square fit and extracted KF parameter are displayed.

The HP 3561 Dynamic Signal Analyzer setup is extensive and allows the user to program all necessary functions needed for measuring noise voltage or noise currents. A typical setup screen is shown in Figure 2.

Figure 1. Typical Spectral Density versus frequency plot.
Spectral Density or Input referred noise versus frequency plots
can be obtained for each bias VDS, VGS, VBS point.

Figure 2. Noise Measurement Setup Screen
for HP 3561 Dynamic Signal Analyzer.

Calibration

It is very important to perform good calibration of the measurement setup and the instrument used. The HP 3561 has an auto calibration feature that can be enabled so that the instrument can perform periodic self calibration. The noise of the pre-amplifier, the noise floor of the measurement setup and the noise of the load resistance must be measured before the device measurement session.

The subtraction of the parasitic noise from the measure data is carried out inside UTMOST. The noise calibration setup screen is shown in Figure 3.


Figure 3. Noise Calibration Screen

 

SPICE Models Supported

SPICE parameter extraction is performed by UTMOST by specifying the model type. UTMOST supports SmartSpice and HSPICE noise models NLEV=0,1,2,3 and the physical BSIM3v3 Noise model (Noimod=2). The traditional noise models have a common limitation that the KF parameter is independent of VDS, VGS and VBS bias. Upon the completion of parameter extraction, KF versus DC bias tables and plots need to be generated.The extracted noise parameters are fed back into special NOISE verification circuits and simulated using SmartSpice. This final step completes the verification of the extracted noise parameters.

 

Flicker Noise SPICE Modeling and Characterization Service

Silvaco offers a cost effective 1/f measurement and SPICE model parameter extraction service.

A noise characterization service can be performed on a wafer or on packaged parts. The customer needs to specify the desired DC bias points and the measurement frequency range. Silvaco will extract the DC and the noise models for each device. Spectral density versus frequency plots are provided along with KF versus DC bias tables (Table 1).

 

Part III - In the next issue a detailed description
of the low noise amplifier will be introduced.