General fabrication facilities include access to sub-micron optical lithography, an optical pattern generator, chemical vapor deposition systems (low pressure and plasma assisted deposition of nitrides, oxides, and polysilicon), reactive ion etch, and bulk micromachining. The high frequency measurement lab consists of three main measurement instruments. Two impedance analyzers and one network analyzer allow on-wafer complex impedance measurements from 100 Hz to 40 GHz. The impedance analyzers measure the real and imaginary part of the input impedance and hence can be used for complex impedance spectroscopy. The network analyzer measures S-parameters which can then be converted to an equivalent impedance.
RF and Microwave Measurement Capabilities
The high frequency measurement lab consists of three measurement instruments. Two impedance analyzers and one network analyzer allow on-wafer capacitance to be measured from 100 Hz to 40 GHz. All instruments have inherent accuracies that effect the overall accuracy of any measurements made. The accuracy is load dependent and frequency dependent.
In addition to limitations in accuracy, each instrument type produces measurement errors that are load and frequency dependent. Figure 1 shows a comparison of typical 10% error contours for four types of instruments. The impedance produce by a capacitive load of 1 and 10 pF value are also shown for reference. As can be seen, for the same load different instruments are most suitable for use at different frequencies. It can also be seen that network analysis is most appropriate when the load has an impedance magnitude near 50 ohms (the reference impedance for the network analyzer).
Figure 1. Comparison of different types of measurement instruments at 10% accuracy. Adapted from HP product literature.
The impedance analyzers measure the real and imaginary part of the input impedance and hence can be used for complex impedance spectroscopy. The network analyzer measures S-parameters which can also be converted to an equivalent impedance network
RF Instruments: Overall frequency range 100 Hz-40 GHz
Measurements made with both impedance meters between 100 kHz and 1.8 GHz can be done with very little set up time (1 day or less) These measurements take 2-5 minutes for a standard configuration. Use of the network analyzer would require several weeks of work and purchase of new equipment. Lower frequency measurements on the 4194 requires a longer setup time (2-3 days) and long measurement time (up to 8 hours ) due to the signal averaging requirements.
High Frequency Wafer Probes
Cascade Microtech ACP40 probes with tungsten tips are used for most measurements. These are fixed tip spacing probes which means that each different probe pad layout requires a different probe. The probes can have two or three tips (one signal and one or two grounds). The probes can be used from DC to 40 GHz.
Pitches available (in mm)
100,125,150,200,and 250 are standard
350,400,500,650,750,1000,and 1250 are available as custom parts
Temperature range -263°C to 200°C
Continuous DC current: 5A max
On-Wafer Impedance/S-Parameter Probe Station