MOSFET 1/f noise measurement under switched bias conditions

Abstract

A new measurement setup is presented that allows the observation of 1 noise spectra in MOSFET's under switched bias conditions in a wide frequency band (10 Hz-100 kHz). When switching between inversion and accumulation, MOSFET's of different manufacturers invariably show reduced 1 noise power density for frequencies below the switching frequency. At low frequencies (10 Hz), a 5-8 dB reduction in intrinsic 1 noise power density is found for different devices, largely independent of the switching frequency (up to 1 MHz). The switched bias measurements render detailed wideband 1 noise spectra of switched MOSFET's, which is useful for 1 noise model validation and analog circuit design.

Interpretation of MOS transistor mismatch signature through statistical device simulations

“…In other words: if the measurement is fast enough, a possible contribution to the mismatch could be suppressed. This is very similar to other experiments where 1/f noise was shown to be reduced when large slow signal (switched measurements) was applied [76,77,78,79].…”

“…Now the impact of interface state "preconditioning" is investigated by comparing pulsed-matching measurements obtained using different pre-soak conditions. Note that it is known from switched 1/f noise measurements that low-frequency noise, and thus most likely the underlying slow oxide traps, are affected by the pre-soak charging states of these traps [78,79]. Figure 3.23 presents fluctuation sweeps of pulsed measurements with the short pulses (1 µs) but using different base levels.…”

Low-Frequency Noise Phenomena in Switched MOSFETs

“…If these conditions are satisfied, a uniform distribution of traps in and results. To explain that turning a device on and off periodically leads to a decrease in the LF noise PSD [5]- [7], [42], we must conclude that the distribution of trap 's is not uniform in . This can be the distribution of 's in a large device with very many traps, but it can also be the distribution of 's over an ensemble of small devices, each with a limited number of traps.…”

“…Since trap densities in MOSFETs are commonly U-shaped in energy [43], [44], this explains that LF noise in MOSFETs decreases when the device is periodically turned on and off [5]- [7], [42]. A circuit designer may expect a large MOSFET to behave predictably in this way.…”

“…2) LF noise in small devices shows extreme variability; measured LF noise can vary by several orders of magnitude between different nominally identical devices [4]. 3) MOSFET LF noise is reduced when the device is subjected to large signal excitation (LSE) [5]- [7]. In other words, turning a MOSFET off for some time before turning it on reduces its noise when it is on.…”