Stock-based compensation expense included in the Company's consolidated financial statements for the three and six months ended June 30, 2019 and July 1, 2018 was as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30, 2019		July 1, 2018		June 30, 2019		July 1, 2018
Cost of revenue	$	18	$	35	$	44	$	69
Research and development		532		207		1,187		390
Selling, general and administrative		241		237		511		452
Total costs and expenses	$	791	$	479	$	1,742	$	911

No stock options were granted during the three and six-month periods ended June 30, 2019 and July 1, 2018. As of June 30, 2019 and July 1, 2018, the fair value of unvested stock options, net of expected forfeitures, was approximately $102,000 and $200,000, respectively. The remaining unrecognized stock-based compensation expense relating to stock options is expected to be recognized over a weighted average period of 2.59 years as of June 30, 2019.

The following table summarizes the activity in the shares available for grant under the 2019 Plan and 2009 Plan during the six months ended June 30, 2019 (in thousands):

	Shares available for grants
	2019 Plan			2009 Plan
Balance at December 30, 2018		-			6,760
Authorized		5,000			-
RSUs granted		(794	)		(3,355	)
RSUs forfeited or expired		184			762
Options forfeited		15			20
Plan shares expired		-			(4,187	)
Balance at June 30, 2019		4,405			-

The following table summarizes stock options outstanding and stock option activity under the 2009 Plan and the 2019 Plan, and the related weighted average exercise price, for the six months ended June 30, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Term		Aggregate Intrinsic Value
	(in thousands)					(in years)		(in thousands)
Balance outstanding at December 30, 2018		3,201		$	2.18
Forfeited or expired		(580	)
Exercised		(4	)
Balance outstanding at June 30, 2019		2,617		$	2.29		3.97	$	-
Exercisable at June 30, 2019		2,383		$	2.43		3.65	$	-
Vested and expected to vest at June 30, 2019		2,594		$	2.31		3.94	$	-

The aggregate intrinsic value in the table above represents the total pretax intrinsic value, based on the Company's closing stock price of $0.58 as of June 30, 2019, which would have been received by the option holders had all option holders exercised their options as of that date.

The total intrinsic value of options exercised during the six months ended June 30, 2019 and July 1, 2018 was $0 as the stock price was lower than exercise price. Total cash received from employees as a result of employee stock option exercises during the six months ended June 30, 2019 and July 1, 2018 was approximately $3,600 and $0, respectively. The Company settles employee stock option exercises with newly issued common shares. In connection with these exercises, there was no tax benefit realized by the Company due to the Company's current loss position. Total stock-based compensation related to stock options was $24,000 and $34,000 for the three months ended June 30, 2019 and July 1, 2018, respectively, and $49,000 and $72,000 for the six months ended June 30, 2019 and July 1, 2018, respectively.

The Company grants restricted stock units or RSUs, to employees and directors with various vesting terms. RSUs entitle the holder to receive, at no cost, one common share for each RSU as it vests. In general, the Company's policy is to withhold shares in settlement of employee tax withholding obligations upon the vesting of RSUs. The stock-based compensation related to RSUs was $756,000 and $382,000 for the three months ended and $1.6 million and $722,000 for six months ended June 30, 2019 and July 1, 2018, respectively. As of June 30, 2019 and July 1, 2018, there was approximately $3.1 million and $2.3 million, respectively, in unrecognized compensation expense related to RSUs. The remaining unrecognized stock-based compensation expense is expected to be recorded over a weighted average period of 1.76 years.

A summary of activity for the Company's RSUs for the six months ended June 30, 2019 is as follows:

	RSUs & PRSUs Outstanding
	Number of Shares			Weighted Average Grant Date Fair Value
	(in thousands)
Nonvested at December 30, 2018		2,570		$	1.23
Granted		4,148			0.85
Vested		(926	)		1.08
Forfeited		(401	)		0.96
Nonvested at June 30, 2019		5,391		$	1.04

As of June 30, 2019, 873,000 shares remained available for issuance under the 2009 ESPP. For the three months ended June 30, 2019 and July 1, 2018, the Company recorded stock-based compensation expense related to the 2009 ESPP of $11,000 and $63,000, respectively. For the six months ended June 30, 2019 and July 1, 2018, the Company recorded stock-based compensation expense related to the 2009 ESPP of $60,000 and $117,000, respectively. The weighted average estimated fair value, as defined by the amended authoritative guidance, of rights issued pursuant to the Company's 2009 ESPP during the second quarter ended June 30, 2019 and July 1, 2018, was $0.31 and $0.47, respectively, per right, respectively.

The fair value of rights issued pursuant to the Company's 2009 ESPP was estimated on the commencement date of each offering period using the following weighted average assumptions:

	Three Months Ended						Six Months Ended
	June 30, 2019			July 1, 2018			June 30, 2019			July 1, 2018
Expected term (months)		6.00			6.0			6.00			6.00
Risk-free interest rate		2.40	%		2.09	%		2.40	%		2.09	%
Volatility		53.77	%		44.76	%		53.77	%		44.76	%
Dividend yield		—			—			—			—

As of June 30, 2019, there was no unrecognized stock-based compensation expense relating to the Company's 2009 ESPP.